Your memory doesn't label where a memory came from

Recalling that something happened is easy. Recalling whether you lived it, read it, dreamed it or just imagined it is a separate — and much less reliable — mental step. When that step fails, imagined events get filed away as real ones, which is part of why a vivid enough suggestion can implant a memory of something that never occurred.

— Marcia K. Johnson, Shahin Hashtroudi, and D. Stephen Lindsay, Source Monitoring — Psychological Bulletin, 1993