Position sizing usually matters more than entry timing for long-run performance. Mechanism: A well-timed entry at too large a size can destroy a portfolio. A mediocre entry at appropriate size survives and lets the thesis work. $$ Max\ Position = \frac{Portfolio\ Risk\ Budget}{Expected\ Position\ Volatility} $$ Plain English: Size should be set by how much risk the portfolio can absorb, not by how confident you feel. Why it matters: That is why professional risk management starts with "how much" before "what" or "when." Market translation: Sizing a single stock position at 25% of the portfolio turns any -20% stock decline into a -5% portfolio hit. At 5%, the same decline costs only -1%. Failure mode: The mistake is perfecting the entry signal while ignoring whether the position size allows recovery from being wrong. Review question: Write down the state variable you would monitor first if this thesis started to drift. The point is not to memorize the label. The point is to know what variable is actually doing the work.