There is actually a rule, and now I finally understand the reason…

On most men’s shirts, buttons sit on the wearer’s right; on most women’s shirts, they sit on the left. One widely repeated explanation points to wealthy women who relied on servants to dress them. Left-side buttons would have been convenient for a right-handed attendant facing the wearer. Men, meanwhile, generally dressed themselves, making right-side buttons practical for right-handed wearers. Another theory connects men’s fastening conventions to carrying weapons, although these explanations should not be mistaken for a single, conclusively documented origin.

What endured was the convention itself. As clothing production expanded, established patterns helped preserve different fastening arrangements for men’s and women’s garments. Whatever combination of customs first shaped them, those arrangements outlasted the circumstances commonly used to explain them. Today, button placement is largely a matter of tradition, not necessity—a quiet reminder that everyday clothing can retain traces of older social expectations long after their original meaning fades.