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A memorable example can be easy to explain after the event. It may still say little about how often the same reasoning failed in cases nobody chose to describe.
Define the full set of cases
Ask which observations qualify for the comparison before selecting the winners. Include unsuccessful, unavailable and unresolved cases where they belong. A list containing only examples still visible today can conceal important omissions.
Count outcomes and their size
In a fictional ten-outcome exercise, nine gains of one unit and one loss of twenty units produce a total loss of eleven units. The high proportion of positive outcomes does not describe the whole result. This arithmetic ignores costs and timing; it is not a trading backtest.
Investigate selection
Was the explanation chosen before the result? How many variations were tried? Which period was excluded? These questions help distinguish a prospectively stated idea from a story fitted to the examples that survived.
Research on backtest overfitting explores one formal version of selection problems in strategy evaluation. Our comparison-group exercise is a simpler way to frame the question, not a replacement for statistical testing.
An incomplete sample can still generate a useful hypothesis. The responsible next step is to gather a better comparison, rather than promoting the initial story into a confident prediction.
