Pardon my complete speculation, but I bet your success factor is "I built ... my girlfriend a tool." My only successful product to this date is an app I built because my wife asked me to. It is in an non-technical domain which I knew nothing about. I thought it was rather non-promising, but, since it was a pet-peeve of hers, I gave it a try. It was an awesome (and very bonding) experience - she explained me the probl…
I really can't say who spent more time (she did graphics, I wrote code) but to this day it's a bit of a sore point to talk about, just that we were both absolutely not happy with the outcome and see it as completely wasted time.