Believe it or not, video games. I play sims for years before I autoX a real car(also had experience autocrossing Formula SAE cars, which were also 2 pedal cars at my school). The first time I went to autoX my MK6 I was planning to brake with right foot until I get comfortable then I will try to brake with left foot. Then first braking zone I just instinctively went left foot brake and never looked back.
I actually don't drive normally braking with left foot. And I kinda consciously do that because I want to separate driving hard for track/autoX to daily driving. I think one time I went to NC/TN area for fun and was following my friend and half way through a stretch of road I noticed I started to left foot brake and I backed off...