Art of War Ch. 6: Where Geometry Fails — The Limits of Jomini for an Investor

"All models are wrong; some are useful. The danger is forgetting the first half." — George Box

Military Context

The first five chapters demonstrate the power of Jomini's system. This one examines where it fails — because a framework shown only succeeding does its greatest damage when it stops working.

1. The Lesson of 1914

Jominian thinking reached its peak at the outbreak of the First World War and collapsed there.

Every general staff held precise mobilisation plans, railway timetables, and geometrically designed offensives. Germany's Schlieffen Plan was the method's ultimate product: victory within weeks through an exactly calculated flanking manoeuvre.

The result was four years of trench deadlock and millions dead. The failure was not insufficient precision but that the plan assumed an opponent who would not react unexpectedly and technological conditions that would not change — machine guns and barbed wire annulled the attacker's geometric advantage.

2. Three Modes of Failure

The third deserves particular attention: an elaborate plan is not merely capable of being wrong, it slows your discovery that it is wrong — because a framework you invested heavily in invites explaining anomalies away rather than questioning the framework.

The Wall Street Translation

3. What This Means for Rule-Based Investing

None of this means abandoning rules. The evidence across this library consistently shows mechanical rules beat in-the-moment judgment in most settings.

It means rules must come with three things:

• Failure conditions — written in advance, stating when the rule no longer applies
• Redundancy — never committing all capital to a single rule system
• Periodic reassessment — checking whether the market conditions the rule depends on still hold

4. Jomini's Genuinely Durable Contribution

Fairness requires saying that Jomini is criticised for over-simplification while his central insights still hold.

Concentration beats dispersion, logistics precedes tactics, avoid frontal assault — these remain correct two centuries later, as heuristic guides rather than computable laws.

That is this book's final position for an investor: treat Jomini as a checklist, not an algorithm.

Actionable Trading Rules

1. Write failure conditions for every rule: before adopting a strategy, state what would make you stop using it.
2. Never commit everything to one system: however good the backtest, any single method can be voided by structural change.
3. Be wary of confidence born of precision: the more elaborate the model, the more likely you are to defend it rather than question it when it errs.

Relevance to a Retirement Portfolio

This chapter's conclusion for retirees matches where the entire Wave 3 series arrived.

A retirement plan depending on precise assumptions — a specific return, a specific inflation rate, a specific market sequence — collapses like the Schlieffen Plan when those assumptions drift. A plan built with redundancy — a conservative withdrawal rate, a cash buffer, international diversification, flexible spending — survives most scenarios without having predicted any of them exactly.

Jomini's geometry teaches you how to attack; retirement planning is fundamentally about ensuring you do not need every attack to succeed.