In no particular order:
Solving "good problems." I define "good problems" as problems we face as a result of our freedom, affluence, or connections with decent people. Having to choose which phono cartridge to upgrade, as an example, in my world is a good problem to have. Another attribute of "good problems" is that the penalties for bad decisions are not severe. Dinging your credit card a bit when expectations were not met by a recent purchase is survivable. The penalties for some other decisions are not. I'm grateful to have "good problems" to deal with.
Being proven wrong. It means I learned something that day.
Staying connected/relevant. Keeping current on what's "real" in the world of high performance audio is rewarding on intellectual and emotional levels. On rare occasions I have the opportunity to submit something that might actually be helpful to others.
You guys/gals. Having frequent contact with high IQ individuals with excellent command of vocabularies whose "antennas" are just a bit more sensitive that most may not make me smarter. It just feels that way sometimes.