I’ve heard from numerous sources that we tend to over-wash our hair. Some even say that if you’re not in a dirty/dusty environment, then you can get away with not washing it at all, or just rinsing with water. In that case it does take a little time for your hair’s natural oils to reach the right equilibrium, but once they do then it’s pretty stable and not gross. I can’t make that particular leap, but I don’t use much shampoo and never “lather, rinse, repeat” which is a total scam. I do let conditioner sit, like @Omar_Little and don’t worry too much about rinsing every last little bit out either, but I usually only condition when my hair starts getting longer and more unruly, which has been the case during Covid for sure.