"I don't know what's good anymore."
We've all had this experience. We work on something so much, for so long, that we completely lose perspective. We're too close to it. We can't tell if something's clear, funny, stupid, or so stupid it's funny. At times like this, it's good to have a few go-to people.
"Hey, what do you think of this?"
You need someone who's smart, has good taste, and will be brutally honest with you. Sometimes it's good to have a few of those people.
"One person I showed thought that the cat kind of reminded her of aliens, because this one time she had a dream about alien cats."
If you focus-group an ad around long enough, you will get some pretty strange feedback. We all know the chronic focus-groupers. Sometimes they're legitimately confused, but often they're just fishing for compliments, or searching for the one person who will tell them that their crap ad is brilliant. Don't be that person.
Have your few trusted brains. Use them as necessary. If they all agree that the ad's not working, take that to heart. But don't take every piece of thinking that you ever poop out and show it around to everyone. It's annoying and, because everyone will have a different take on it, it will just confuse you.
As much as learning how to come up with a good idea, you need to learn to evaluate a good idea. Trust your gut. And when your gut is full, trust the guts of a few smart people around you. But don't trust the guts of everyone in the school, or everyone in the agency. That just leads to a big, gooey, gross, gutty mess.