Electronics, once you realize that you can pretty much build anything you need if you can find a chip for it you're unstoppable, at least as long as you can gather the energy to work on it (or to finally fix your broken soldering station)
I almost started out with keyboards, but I ordered a kit from gboards.ca (fully expecting there to be delays), and the person behind that just went poof, and so did the money :/
In the meantime I've been playing around with my g305 mouse (ported ZMK to it, no sensor driver yet) and some other projects, but I still want to build a split at some point, I even have the switches laying around already.
Agreed. I started out with one of those cracker box amplifiers because it looked nice. Then I figured I need something to actually play so I naturally had to build a cookie box banjo with a piezo element for noise pickup. That was a fun trip into a weird rabbit hole.