Pretend your memory is a hash table. You forget stuff because too much crap gets stored under the same few keys. So all the stuff that's mostly the same gets blended together in your memory. If you want to remember, the memory has to be unique. And those techniques are supposed to make things stand out.

That's why things people told me yesterday get blended together, but I'll probably be stuck remembering the "purple monkey dishwasher" thing for the rest of my life, even though I haven't seen that show in a decade or so.