In a famous story, Cicero wrote of Diagoras, an atheist who, when confronted with paintings of people who prayed and then were saved from a shipwreck, replied, "I see those who were saved, but where are those painted who prayed and drowned?"

Survivorship Bias is the error resulting from systematically focusing on survivors (successes) and ignoring casualties (failures) that causes us to miss the true base rates of survival (the actual probability of success) and arrive at flawed conclusions.

To avoid the trap, we must consider the unseen evidence just as much as the seen. To develop a better perspective on base rates of success, consult a Possibility Grid, which lays out completed and not completed actions of both winners and losers.