I mean, maybe it's a bit much to assume everyone has been in a for the most part a positive and fruitful relationship, but the whole "Instead of liking him because he's cute, I think he's cute because I like him" really hits the nail on the head, or at least it does for me.
That sort of mentality definitely starts to take over the longer you are together with someone you genuinely cherish. In fact, it can be pretty hard to cope with at times as your mind starts to whitewash away their negative traits depending on how smitten you are with them, and it can make you unable to see bad things coming ahead...