When you become a parent your whole life changes, including the parenting memes you find funny.
There’s just something about suddenly becoming responsible for the survival and thriving of one or more weak, tiny, idiots that has a totally transformative effect on a human being. Your goals change, your routines change, and you learn how to live without sleep for several years on end. Needless to say, the effect on a parent’s psychology is enormous as is the ensuing stress.