Thanks to Sascha & Petteri for chiming in with more great advice!

The process of refinement happens at all skill levels for as long as you play.  It takes a lot of mental effort & dedicated repetitious practice time.  There's always more to learn and there's always older skills & ideas you have to spend time maintaining or they can decline.

I've been playing for close to 50 years & there are still days I struggle to get things right.  To play a line cleanly or a make chord change consistently without hitting a big clam.  But after enough time & practice I play it right, then it seems so simple & easy. 

Some of this is the brain forming new neural pathways to do certain new fine motor skills, what we commonly call muscle memory.  And that takes practice & time.  As adults we are used to doing things right immediately & getting them done.  Learning new skills requires the patience to realize that you are going to struggle, stumble & basically suck at it until you gradually get better.  So, it can help to enjoy the process, to enjoy it as a challenge & know you aren't going to do any of this easily & immediately. 

You keep working on it until you get it.  And it takes as long as it takes, so you might as well enjoy the ride.

"Music is enough for a lifetime, but a lifetime is not enough for music." - Sergei Rachmaninoff

Keep practicing!