>I find this to be another under-discussed challenging of parenting: you can never even entertain the idea that "maybe this wasn't what I wanted"

Because there's no point in thinking about it. Your wife will ask if you want to leave, your children will hate you, and society will hate you, it will make you feel depressed, and meanwhile it won't accomplish anything. It's a dialogue only for yourself, once you acknowledge that, it becomes far less challenging to deal with and you can move forward with dealing with challenges in solvable ways.