Memories Are Unreliable

Every recall reconstructs the memory rather than simply replaying it, and each reconstruction is an opportunity for new errors to creep in. Recalling a memory can subtly alter it, so over time your most vivid, most confident memories may differ from what really happened. (This isn't a reason to avoid recalling things — actively retrieving information is one of the best ways to strengthen it — but the version you rebuild is never guaranteed to be faithful.)

Psychologist Elizabeth Loftus showed that entirely false memories can be implanted through suggestion alone. In one landmark study, about 25% of subjects became convinced of a fabricated childhood event — being lost in a shopping mall — that never occurred. Your brain genuinely cannot tell a true memory from a well-constructed false one.