For purposes of applying this to golf:
"What comes after the idealism of the beginner's mind?"
I'd say reality or realization. You realise it is hard, complicated, demanding, etc. You realise it isn't as easy as it looks. In this, I assume the 'beginner' first never played the game and takes it up because it looks ideal, appears effortless, or just seems like a nice environment in which to recreate, etc. The ideals are all present for the beginner; look, feel, observation of fun or pleasant task. But, once the beginner is into it, reality sets in. There is where the crux of who sticks with it comes into the process. One can become cynical from that point of reality setting in if they are either not up to the challenge, or just don't like it in some manner that repulses the senses, if you are wired that way. But, I also think you can become cynical after the reality sets in about the nature of the endless pursuit of 'doing it well' , but still continue to pursue it for your own version of fun, challenge, or other motivating factors.