The Piano has definitely been the most complex skill I have been attempting to learn, and I think it has helped me in other areas of my life without me knowing it. I have been able to pick up Premiere pro really quickly and have built a lot of grit towards doing hard things.
I have recently started working on reviewing some older pieces that I had once upon a time learnt, and now I am re-learning them and its going much quicker then the first go around. But now it is a matter of getting it stored into long term memory by using space repetition. I am going to be implementing the forgetting curve on all of the learned songs so I can keep them forever in my head :)