This writing exercise is one of dozens of good ones from "The Making of a Story" (A Norton Guide to Creative Writing) by Alice LaPlante.

Doing this exercise will help open things up.

The goal is to pinpoint previously unexplored material that is still emotionaly important to you and may be tapped into for writing.

Think back and find things that have stuck in your mind, but for no apparent reason. Choose something small, no earthshaking events like deaths, births, or other turning points. Then write them out in detail, making your first sentence "I don't know why I remember..." Don't try to rationalise why you remember it or try to figure out its significance, just put the reader in that place and time.