In March 2009, the S&P 500 fell to 666 — a peak-to-trough decline of 56% from October 2007. The headlines were uniformly catastrophic: bank insolvencies, GM bankruptcy, unemployment heading to 10%, the system genuinely on the brink. Most retail investors sold during this window — Vanguard's 401(k) data showed inflows reversed sharply in Q4 2008 and Q1 2009.

The investors who DIDN'T sell — the ones whose written allocation rules said 'don't change strategy in response to market events' — were the ones who captured the 2009-2020 ~5x bull-market run. The difference between the panic-sellers and the held-through-it cohort wasn't intelligence or timing skill; it was whether they had a written framework that bound their behavior during the moment of maximum stress. This lesson is about that framework — the Investment Policy Statement — and the rebalancing discipline it enables.