One of the most painful experiences in any creative act is when a project loses funding. When a project dies due to circumstances completely out of your control.
Here's a little bit of perspective on that.
Michelangelo's David is housed in the Accademia di Belle Arti di Firenze. In that same museum, the hall leading up to the David in fact, there are four partially-carved sculptures outside of that room called the Unfinished Slaves.
They are sculptures he started but had to abandon due to a lack of funding. Funds dried up. The marble remained uncarved. And his backers were the big corporations of the time: wealthy Italians and The Catholic Church.
The Catholic Church. Bankrolled by God!
And although these events may seem tragic, they're only partially so. Because these projects lost funding Michelangelo pursued other things. Went on to paint the Sistine Chapel. That's a pretty good next step.
There are countless other people/projects this has happened to. Good people, who probably deserved the money more than someone making the Wheaties ad that will "change Wheaties ads forever".
So it might be okay that some projects lose funding. It might be okay that things don't work out this time (so long as it's not every time). Because eventually things will. And if you're able to come up with something "brilliant" once you should be able to do it over and over again. Despite setbacks.
Persistence and taking advantage of the times that do work out are the keys to creating anything. Those are the only things we have complete control over.
Now I'm not saying anyone who works in advertising will do something on the level of Michelangelo. Ours is impure art at it's best. But why not try to do something like that? Something with the impact and the gobsmacking beauty of seeing that ceiling? That is evokes such an emotional reaction? There have been ads that have that effect on me (and the public at large) once in a rare while.
It's worth attempting. Worse that happens is that the funding dries up.