Use to re-prioritize: before attacking a hard problem, ask what about your own last attempt was the real obstacle. Use when 'know thyself' is treated as optional alongside 'know the market' — Musashi says it comes first.

Sun Tzu's famous formula is 'know the enemy and know yourself' — a conjunction, self and enemy side by side. Musashi reorders it into a sequence: self first, enemy second, and frames it as daily competition against your own past self. It's the same insight with a different center of gravity — the individual's craft, not the general's intelligence.