The market-timing reality-check

Good at: The honest baseline: staying invested captures the few unpredictable days that drive most long-run returns.

Fails when: You step out and miss the best days — which usually costs more than the crashes you dodge.

Good at: Riding sustained trends — a golden cross keeps you on the right side of a long move.

Fails when: Choppy, sideways markets, where it whipsaws and bleeds; it also rarely beats buy-and-hold on raw return.

Good at: Range-bound markets — fading overbought and oversold extremes as price reverts.

Fails when: Strong trends, where "overbought stays overbought" and the rule sells far too early.

Good at: Mild context — there are real, documented calendar tendencies (weak September, stronger winter).

Fails when: Used as a system: the edge is small, noisy year to year, and eaten by costs and taxes.

Good at: Setting expectations — knowing a 50% fall needs a 100% gain keeps you patient and invested.

Fails when: Ignored — panic-selling near the bottom locks in the loss and misses the rebound.

Good at: Major extremes — buying peak fear and trimming euphoria, especially in ranges.

Fails when: Mid-trend — the crowd stays right longer than you can stay solvent betting against it.

Good at: Lowering regret and timing risk — a disciplined way to invest a sum without betting on one date.

Fails when: Judged purely on returns: in rising markets lump-sum usually wins (more time invested).

Good at: Removing emotion and smoothing the ride by combining a few robust signals.

Fails when: Over-tuned — every extra weight and threshold is a chance to curve-fit the past into a fragile rule.