Men’s shirts have buttons on the right and women’s shirts have buttons on the left. I have often worn men’s shirts but it always feels weird to have buttons on the other side.
One theory is that men’s and women’s shirts button from different sides because most people are right handed and many centuries ago, buttons were for richer people. Thus most women who wore buttons were dressed by right-handed maidservants, while men dressed themselves.
Regarding men (whose shirts flap left to right), armour used to overlap from left to right to keep your shield side (left) doubly protected. Because most people were right handed, the shield was on the left arm and the weapon was in the right hand – also a reason that many countries drive on the left. This was because you held your weapon in your right hand and so your weapon arm was always closest to those approaching by horseback in the opposite direction.
I wonder what happened in those days if someone was left-handed. Were they ostracised? And do jeans have the same convention?