Why is not enough to be happy and content with life? Honestly, I have no idea and it seems this question torments others as well. "Daydream" by Doctrines is about the consciousness of a person who is in a state of great uncertainty and emotional stress due to the thoughts that go in and out of his mind.
"I catch her eye, I think of your for a second, get embarrassed and close my eyes".
Is it over once you have impure thoughts of someone else than your partner, though you don't act on them? I would say no unless they come on a daily basis and at one point you start avoiding direct eye contact while having sex and fantasizing it's the gift-shop girl that is heavily breathing in your neck. Do not worry as "It was only a Daydream! It was only a daydream!"