A lot of my significant personal improvement happened as a result of highly measurable progress and tight feedback loops. For example:
Speedcubing. I don't recommend it, though—I started about a year ago and it sniped a significant amount of my free time in 2014, on the order of 400-500 hours. (I had a similar experience with Go in college.)
A lot of my significant personal improvement happened as a result of highly measurable progress and tight feedback loops. For example: