Signal half-life matters as much as signal direction. Mechanism: A signal that points the right way but decays quickly should not be traded with the same holding period as a slow structural signal. Time is part of the thesis. If the horizon changes, the execution logic should change with it. Market translation: A short-horizon mean reversion signal on $QQQ is a different object from a medium-term trend-following process on the same ETF. $$ Signal\ Value_t = Signal_0 \cdot e^{-\lambda t} $$ Plain English: Some signals lose explanatory power quickly, so old information should get less weight. Failure mode: The expensive error is mixing a fast entry logic with a slow stop and calling the result "conviction." Review question: Ask whether the market is mispricing the mechanism or simply narrating it loudly. The point is not to memorize the label. The point is to know what variable is actually doing the work.