You have to have it to lose it. I'm still working on the first part.
If I move on to work on something new: A new song or new technique I can go blank on what I previously had down in a week. Of course it only takes a moments work to get it back.
I'm like Hansel & Gretel dropping bits of songs & guitar moves on the path blissfully unaware that a species of wild-throated note-snatchers are native to my brain.