It’s the animal instinct to reproduce. In order to have the urge to reproduce, one must believe (even if subconsciously) that there’s something desirable to replicate and pass on.
Even the ugliest people and the dumbest people think that they have something worth passing on (kindness? compassion?).
You think that your kids are special when in fact they are just ordinary.
Parents of criminals think that their kids should be forgiven and will do everything to save them. On the other hand, strangers want those people locked away for life or even executed.
When a man gets married he thinks that his wife is a great catch. If your hear men talk about women, you’d wonder how they can possible get into bed with their wives at night.
If a woman looked in the mirror and believed that she was below average then what’s the point of reproducing?