You know the move that worked once. The joke that landed. The negotiating tactic that closed the deal. The way you handled the last crisis. So you reach for it again. And again.
It's comfortable. It's proven. It's yours. And somewhere in there, without noticing, you've stopped responding to what's actually in front of you and started responding to a memory of what used to be in front of you. The world moved. You didn't.
Robert Greene's second strategy names this precisely: fighting the last war.1 It isn't about literal battles. It's about the mind's habit of repeating whatever formula succeeded before, applying it to a situation that has already changed shape.
The remedy Greene proposes isn't more knowledge. It's guerrilla war on your own mind: no static defenses, no fixed doctrine, everything kept fluid enough to respond to what's actually happening right now.
The chapter's central case makes the mechanism concrete. In 1806, Prussian generals — trained under the legendary Frederick the Great, drilled for decades in his precise, disciplined tactics — went to war against Napoleon convinced he was a lucky amateur who'd crumble against real military science.1
Prince Hohenlohe, one of their most senior commanders, had spent his career studying Frederick's playbook and planned to execute it against the French to the letter. Napoleon's army, by contrast, carried its own supplies instead of relying on slow wagon trains, moved with a speed the Prussians hadn't accounted for, and adapted formation on the fly instead of executing a rehearsed maneuver.
At Jena, the Prussians marched into an open field in perfect parade order — a ritual dating back to Frederick himself — while French soldiers picked them off from behind garden walls and rooftops.1 The Prussian army, once the most feared fighting force in Europe, collapsed in a single afternoon. Not because they lacked discipline or courage. Because their discipline was aimed at a war that no longer existed.
Here's what Greene wants you to sit with: this isn't a story about the Prussians being bad generals. It's a story about what happens to any mind, including a very well-trained one, once repetition replaces creativity.
"As we grow older, we become more rooted in the past," Greene writes. "Something that has worked for us before becomes a doctrine, a shell to protect us from reality."1 The shell feels like competence. It's actually the opposite — a substitute for the harder, riskier work of reading the present moment fresh each time.
Napoleon himself, asked what principles of war he followed, said he followed none. His genius, such as it was, lay entirely in responding to circumstances as they actually were.1 "My only principle is to have no principles" is Greene's gloss on this, and it's worth taking literally rather than as a paradox to admire from a distance. The discipline isn't in having no framework at all. It's in refusing to let any framework calcify into something you apply without checking it against what's currently true.
Greene's own "Keys to Warfare" section for this strategy names four specific sub-tactics, each illustrated briefly, worth holding separately from the main Napoleon/Hohenlohe case because they operate at a smaller, more personal scale.
Erase the memory of the last war. North Vietnamese general Vo Nguyen Giap had a rule: after every successful campaign, deliberately convince himself it had actually been a failure — not out of false modesty, but as a discipline against complacency.1 The baseball hitter Ted Williams did the tactical equivalent every at-bat, forgetting the last swing — home run or strikeout — the moment he got back to the dugout.1
Keep the mind moving. Greene points to the childlike quality shared by history's greatest strategists — Alexander, Napoleon, Musashi — all unusually quick to forget the past because the present held their full attention.1
Absorb the spirit of the times. Joan Crawford's Hollywood career, unusually long for an actress of her era, survived by constant stylistic reinvention — siren, noir heroine, cult queen — rather than clinging to whatever had made her famous first.1
Reverse course. Fyodor Dostoyevsky, prone to depressive stagnation between the bursts of ecstatic clarity his epilepsy brought him, would deliberately gamble away all his money at a casino to force himself back into a state of urgent, unroutine thinking.1
The swordsman Miyamoto Musashi runs the identical logic at a completely different tempo — not a career-spanning military doctrine, but three separate duels, each won by refusing to repeat whatever had worked in the last one.1
Against the Yoshioka clan's Matashichiro, who expected Musashi's usual late arrival, Musashi came early and struck first. Against Baiken, whose sickle-and-chain had never been beaten, Musashi fought with two swords instead of one — a combination Baiken had never faced and couldn't calculate against. Against the great swordsman Sasaki Ganryu, Musashi arrived deliberately late, armed with a carved wooden oar instead of a sword, and won through psychological disorientation before a single blow landed.
What connects the three isn't a technique. It's the absence of a repeated technique. Musashi's own writing names the failure mode directly: "It is a disease to be obsessed by the thought of winning... to be obsessed by the thought of using everything you have learned."1 Even fixation on your own hard-won skill, applied reflexively rather than freshly, is a form of fighting the last war.
There's a reason the Prussian generals didn't just casually miss the signs — they had ten years of them and still didn't move. Abandoning a formula that has worked isn't a neutral cognitive update. It costs something real: the years spent mastering it, the identity built around being the person who knows this method, the social standing that came from being its expert.
Hohenlohe wasn't just choosing between two tactics. He was choosing between a war he could win by being exactly who he already was, and a war that might require becoming someone else entirely — someone whose expertise counted for less, whose decades of study might not transfer. Framed that way, the generals' choice looks less like stupidity and more like a bet nobody wants to admit they're making: better to lose gloriously as the expert I already am than to win clumsily as a beginner at something new.
This is worth naming plainly, because Greene's chapter treats the failure mostly as a perceptual one — a failure to see reality clearly. It's also a motivational one. Updating your method sometimes means admitting your specific, hard-won competence just became worth less. Nobody does that willingly, which is exactly why it has to be forced rather than invited.
You don't need a battlefield to run this trade-off. A manager who built her reputation on being the person who catches every detail personally faces the identical bet the moment her team doubles in size: keep reviewing everything herself (the formula that made her indispensable) or delegate real authority (the only thing that actually scales, and the thing that makes her personal detail-catching no longer the team's bottleneck). The second option is strictly better for the team. It's also, structurally, Hohenlohe's choice — trade a competence that defines you for a method that might not need you in the same way.
You've closed the last three negotiations the same way. Open firm, concede slowly, land somewhere in the middle everyone can live with. It's worked well enough that it's become automatic; you barely think about it anymore, which is itself the first warning sign.
This next one feels different in some way you haven't quite named, and you catch yourself reaching for the same opening line anyway, because it's comfortable and it's yours.
Stop before you send it. Ask the Hohenlohe question: what actually changed since the formula last worked? The other side has a new decision-maker this time, someone who wasn't in the room for your last three deals and has no memory of your pattern being reasonable.
Opening firm against someone with no context for why you'd do that doesn't read as strategic. It reads as aggressive, because there's no shared history to soften it.
You adjust: open with context instead of position, the way Musashi swapped weapons rather than technique when the opponent changed. The old formula wasn't wrong last time. It's wrong now, for this room, against this person — and the only way to know that is to have actually looked instead of running the tape from memory.
The Jena case is strong because it's overdetermined. Multiple independent signals (recent poor performance, internal reform voices, a decade of documented evidence about Napoleon's methods) were all available to the Prussians beforehand, and Greene is right that they chose the comfort of doctrine over the discomfort of updating.1 The Musashi material is more anecdotal — three famous duels retold from samurai legend, useful as illustration but not independently verifiable in their specifics.
The open tension the chapter doesn't resolve: Greene's own Reversal admits the limit of the advice directly.
"There is never any value in fighting the last war," he writes, "but while you're eliminating that pernicious tendency, you must imagine that your enemy is trying to do the same."1
Saddam Hussein invaded Kuwait believing America was still fighting its last war — paralyzed by Vietnam-era casualty aversion — and was wrong precisely because he assumed his opponent, too, was stuck in the past.1 This means the strategy has a hidden second-order requirement the chapter's main body underplays: it's not enough to avoid fighting your own last war. You also can't assume your opponent is still fighting theirs. Two live, adapting minds facing off is a much harder problem than the clean Napoleon-vs.-fossils framing suggests.
Put this beside Weak Traits Are Self-Maintaining (Greene, from Laws of Human Nature), which argues that strengths decay without active practice while weaknesses persist on their own.
The Guerrilla-War-of-the-Mind Strategy supplies the missing mechanism for exactly why a strength decays: not from disuse, but from overuse without renewal. The Prussian army's discipline was practiced constantly, relentlessly, and decayed anyway, because what was being practiced was the doctrine itself rather than the underlying skill of reading a live situation.
Read together, the two pages suggest that "keep doing what works" and "stop doing what worked before" aren't actually contradictory advice. The first applies to the skill of adapting. The second applies to whatever specific tactic that skill most recently produced.
Creative Practice → Artistic Reinvention Under Repetition Fatigue. Joan Crawford's own career, referenced in this same chapter, survived Hollywood's brutal short shelf life for actresses precisely by refusing to fight the last war stylistically — moving from siren to noir heroine to cult-horror queen as the industry's tastes shifted underneath her.1
The insight the pairing produces: what looks like inconsistency from outside (an artist who "keeps changing") is frequently the opposite of fighting the last war — it's the actual discipline. And what looks like consistency (an artist who "found their style and kept it") is frequently a slower-motion version of Hohenlohe's mistake, mistaking a formula that worked for a permanent law.
Psychology → Cognitive Rigidity and the Einstellung Effect. Problem-solving research on the Einstellung effect documents that once a mind has solved a class of problem with a particular method, it will keep reaching for that method even when a simpler, better solution is available — the prior success actively blocks perception of the better option.
The insight the pairing produces: Hohenlohe's failure wasn't a uniquely military phenomenon or a personal character flaw. It's the default behavior of trained cognition under uncertainty, which means the "guerrilla war on your own mind" Greene prescribes isn't optional maintenance. It's the only known countermeasure to a bias built into how expertise itself forms.
Notice that the artistic-reinvention case and the Einstellung research are describing the same underlying fact from two different altitudes. Crawford's career shows what successfully fighting the bias looks like from outside — a visible string of style changes an audience can track. The cognitive-science handshake shows why that visible pattern is actually rare: the bias isn't a quirk some people have and others don't, it's the default setting of any mind that has ever gotten good at something. Crawford wasn't unusually free of the Einstellung effect. She was unusually disciplined about fighting it, cycle after cycle, in a industry that punished her instantly and visibly every time she didn't.
Your past successes are not a bank of experience you can draw on indefinitely. They're the most dangerous trap in your own arsenal, because they're disguised as competence. The Prussian army wasn't undisciplined or poorly led. It was extremely disciplined, extremely well led, by the standards of a war that had already ended.