> He knows a lot about his domain, sure, but he's no god and there are a lot of areas he knows diddley-squat about.... user interface design for one!

And Einstein knew nothing about biology.

I'm sure he knows "diddley-squat" about most areas, but as long as he knows a lot about his domain then he's an expert.

And he is good at user interface design, and git is a good example of that; it's just not aimed at beginners. It was designed by and for expert users, and the interface fits that very well.