In fact it was not even a hobby at the beginning. It was just me unable to have what I want (sometimes I don't find it in stores, sometimes my parents say "no") so I do it myself. This is the exact same thing that led me to programming, my parents telling me they won't buy me a GameBoy and me (years later) programming it on the thing I have that looks most like a GameBoy.
But yeah, I agree that sometimes I built things I didn't really want, just for the sake of it, like the tank.