Slippage is not random bad luck; it is a measurable cost with identifiable drivers. Mechanism: Slippage comes from order size relative to available liquidity, timing, venue choice and information leakage. Each driver can be managed. That matters because slippage that looks small on one trade compounds into a significant return drag over hundreds of executions. Market translation: A market order on a mid-cap stock during low-volume hours can cost 15-30 bps more than a patient limit order during the liquidity window. $$ Implementation\ Shortfall = Decision\ Price - Execution\ Price $$ Plain English: Implementation shortfall measures the gap between the price you decided to trade at and the price you actually got. Failure mode: The mistake is accepting slippage as the cost of doing business without analyzing which part is preventable. Review question: Ask whether the market is mispricing the mechanism or simply narrating it loudly. That is usually where the edge is: not in the vocabulary, but in the structure underneath it.