How I Met Your Mother, Season 1

[Lily admits to Ted about the arts program and how it could derail her and Marshall's wedding]

Lily:
There are certain things in life where you know it's a mistake but you don't really know it's a mistake because the only way to really know it is a mistake is to make that mistake and look back and say, "Yup, that was a mistake". So really, the bigger mistake would be to not make the mistake because then you'll go your whole life not really knowing if something is a mistake or not. And damn it, I made no mistakes. I've done all of this: my life, my relationship, my career mistakes-free. Does any of this make sense to you?

Ted:
I don't know, you said 'mistake' a lot.