Having A Baby
According to this person, there’s no such thing as being ready for a baby. Even if you’re one of the most mentally and financially stable people in the world, nothing will take you down like having a kid. And just when you think you’ve got the hang of it as most arrogant people do, the baby will begin crying or teething, or somehow change the game all over again.
It’s one way to take your confidence down a few notches. That’s why most people wait before having kids, or never even have kids in the first place (via Constative).