Coffee. Anyone can make a cup of coffee. Making a good and properly prepared cup of coffee, espresso, etc. is surprisingly complex.

I wanted to make myself a simple cappuccino at home. I now have several pieces of prosumer gear, gadgets, fancy beans, and spend my free time reading up on things like coffee grind distribution methods, hacking my machine to add a PID, and other such ephemera. On the plus side, I'm saving several hundred dollars a year on my coffee habit despite all the toys, so there's that.