I performed my last recital for my degree program in 2004 (has it really been that long?) and, while I love the repertoire I programmed, if you asked me to perform it today, or even next month, I doubt I could do it. The same could be said for some jazz standards I knew once upon a time but have since been relegated to the attic of my practicing. I have to ask myself if it was really worth all the hours I spent trying to master those pieces.
In describing what he calls the "Law of the Harvest", Stephen Covey cites performing on a musical instrument as an example of an endeavor that you can't fake your way through. You have to invest your energy over the long haul in order to attain a high level of performance. This is in contrast to the academic plague of cramming for a test, only to dump everything you "learned" on the test page, most of which stays there instead of in your head. Or faking your way through short-term social interactions with a few slick tricks that won't hold up under closer inspection.
If we don't do something to retain what we have worked so hard to attain, is what we do really any different than cramming for the next exam?