Sometimes the obstacle to happiness and learning is not that you don't know how to do something. It is that you used to. You have already been through the first 100 hours. For whatever reason life gets in the way and something that used to be a great source of fulfilment ceases to be. You need to get back to where you were. To get there though, you have to start again. Muscle memory is a wonderful thing. The first time I did the Midmar Mile in 1996, I knew how to swim but was absolutely shattered after a few lengths of the 50m pool when I started training for it. I realised I quite liked swimming and so joined the team in my last year of high school. Very much an outsider, but not being good at things has never stopped me from doing them if I enjoyed it. I didn't do a lot of swimming after school, but when I decided to do the race again in 2006 I was able to swim a mile fairly comfortably on the first day back in the pool.
I am sure a lot of this is mental. Real swimmers will also tell you that a mile isn't actually that far. My point is just that once you have done something, it can be easier to do it again even with a big gap. For other things, the big gap can be an obstacle. I know quite a few people who at some stage have given up a musical instrument. Some don't want to play again now because they can't play at the level they used to. When they were at school they had lots of time to practice, and they know that a certain level of physical fitness is required (strong fingers, calluses etc.). I would love to know whether music and swimming share a similar level of muscle memory. Can you reach a reasonable level again with less effort? Can you reach a level where you find flow?
Widening the thought a little, childhood is a time when you got to experiment with lots of things. You can't do everything though, and so often you give something up to take up something new. One way to find hobbies or sources of flow is to think back to all the things you did and try remember which ones gave you the most joy? I would love to hear from some people who try to find 100 hours to commit to rekindling an early love. What obstacles are there to getting that back?