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I'm trying to find the name and/or author of a story I read in the 1990s (I think) about a future where everyone takes 'memory loss' pills. It means you only remember three days of short term stuff, though you remember all the basic skills like talking and tying your shoelaces, and who your family is. If you don't take the pills you have to live in an exile community. This boy takes the pills, and is looking after a small shrub, but he doesn't know for how long he's been looking after it. Something like that.
Anyone read something even remotely like this and could point me in the right direction?