Picking up new hobbies, investing in them far beyond what would be considered a casual interest, then getting bored or disillusioned with the community after 6-24 months.
See
Foam dart blasters
yo yos
magic the gathering (This was like 15 years)
coin collecting
juggling
pocket knives
archery
running
Currently working on 3D printing, though that's been more of a means to get back into foam blasters because it's far cheaper to print your own blasters and mod parts.
I'm currently in this cycle as well. Ever since getting a job I don't have the time and energy to consistently do something every day, but I do have a lot more money. Given this lack of energy and consistent time, I just go until the period of rapid learning stops and then I become overambitious and lose interest. I think I mostly understand what causes it, but I'm unable to fix it. Once I see what "the pro's" do I become way to ambitious and ruin the fun.
At least I've been able to keep up running as a hobby, which beats sitting still all day.