Anyone who has fallen in love realizes this is so true.
It reminds me of that old "Star Trek" riff, where Kirk talks a sentient bomb out of destroying the ship by programming it to believe that everything he says is a lie, and then saying, "I'm lying to you."
You fall in love with someone. You think, well, they're not perfect, but maybe I can change them into something better. Meaning, something you didn't fall in love.