Hindsight bias

Hindsight bias is the tendency, after an event has already happened, to believe it was obvious or predictable all along, even when it genuinely was not foreseeable at the time. In investing, this shows up constantly with market moves. After a crash, it is easy to look back and list all the warning signs that seem obvious in retrospect, even though very few people actually acted on them before the decline happened.

The distortion matters because it changes how investors judge their own decision making. If a past outcome feels like it should have been predictable, a subsequent loss can feel like a failure of judgment rather than a reasonable decision that simply did not work out, which can push an investor toward excessive caution or false confidence about spotting the next one in advance.

A useful check against hindsight bias is keeping a written record of an investment decision and the reasoning behind it at the time it was made, rather than relying on memory after the fact. Comparing an actual note made at the time to how the decision gets remembered later often reveals just how much cleaner and more obvious the past looks in hindsight than it ever did in the moment.