I honestly have no idea. I'm pretty sure I can get on and off from either side, likewise I don't think I have a preference for clipping in or out with either foot. I reckon it just depends on where the bike is and what is most appropriate/convenient at the time. I know that if, for some reason, I can't clip in then I'll try with the other foot rather than do battle.
I guess it's experience; as the same man also said "these things take time"