Have a little courage.
Don't be a fucking coward.
There, I said it. But then again, I pretty much always say that, so stop freaking out.
In our line of work we're required to back everything we do with a reason, a meaning and a purpose. Sometimes that can feel like a bit like being corralled into a mediocre outcome–and sometimes it's exactly like being corralled into a mediocre outcome.
In my *ahem* humble opinion, it's the responsibility of both the creative and the client to collaborate on what's possible, striving for a minimum of 'good' while pushing back the things we're told are 'impossible'.
A good creative should be able to see the boundaries and come up with something that leans on them, but doesn't set off the alarms – Day in, day out. It won't make great art, but it will meet the brief and achieve the client's goals.
On the other hand great creative runs at the wall like it's just not there. But without the support of a brave client–someone who'll hit the wall with a sledge-hammer for them just as they 're about tho hit it–they'll just keep running at the brick wall - like some twisted scene from a Harry Potter film (Yeah, I just went there).
Long story short: Trusting each other is paramount in developing really creative work. You have to believe that you've got each other's backs. That takes courage, but it can really pay off.