I once heard an agency owner say, "Miller, it's easy to come up with a great idea. You just have to come up with enough ideas."
Those words sounded simplistic to a 27 year old, but they ring true today. I find it helpful to generate a lot of ideas and not get attached to any one of them. Typically, the agency or client will gravitate to several before choosing their favorite.
I am collaborative and diplomatic about ideas and scripts. The people I work with are very bright and imaginative, and collaboration brings out our collective best.
However, things may not always work out perfectly.
I once helped an entertainment agency pitch the relaunch of a TV show. My idea felt right to a limited audience of one, me. The agency didn't get it and I had zero leverage, so we kept cranking out more ideas. A month later, the agency didn't get it in a different way. Another agency won the account with the same idea I had proposed.