For most people, learning something might take time and practice. Once learned, it will stay with you as long as it's of any use. If not, then it'll be 'forgotten' by long terms. Say for example, when you imagine you'd stop riding your bike for around 5 years, it might take a little practice again to get to the 'level' on the road you once were. The same thing counts for JJ2 (at least for me), as it took me a while to get used to JJ2's online gameplay and 'special moves' using clan training, yet at times I get active at the game, I do have to play a while to 'remember' everything I once learned.

This is just a literal point of few but haha.