Why napoleon was painted with his hand in his shirt?

There are various hypothesis, among them this one. It was considered more decent than letting the hands fallen or crossing the arms at a time where trousers had no pockets. It can also be considered like a pure gesture : the fine orators were represented like this since Aeschines.

@topffer another theory was that painters had difficulty painting the hands, being sort of a portrait painter myself I would attest to that, I bought a small book solely dedicated to painting hands when I was learning how to paint knowing how hard it was especially in the realism style where you have to paint the position of the hand, digit amd nails to the last detail but still I would debunk this theory. The Emperor at the height of his power could commission the finest French artists to depict himself as he wanted to and painting hands was easier than eating peanuts for them

@louievill I think also that David was not afraid by hands. The level of details is impressive here. I do not understand what Napoleon holds in the left hand, but he was holding something.