Dani Shapiro’s Still Writing speaks to the necessity of failure and uncertainty in the creative process:

When writers who are just starting out ask me when it gets easier, my answer is never. It never gets easier. I don’t want to scare them, so I rarely say more than that, but the truth is that, if anything, it gets harder. The writing life isn’t just filled with predictable uncertainties but with the awareness that we are always starting over again. That everything we ever write will be flawed. We may have written one book, or many, but all we know — if we know anything at all — is how to write the book we’re writing. All novels are failures. Perfection itself would be a failure. All we can hope is that we will fail better. That we won’t succumb to fear of the unknown. That we will not fall prey to the easy enchantments of repeating what may have worked in the past. I try to remember that the job — as well as the plight, and the unexpected joy — of the artist is to embrace uncertainty, to be sharpened and honed by it. To be birthed by it. Each time we come to the end of a piece of work, we have failed as we have leapt — spectacularly, brazenly — into the unknown.

F. Scott Fitzgerald famously wrote:

The test of a first-rate intelligence is the ability to hold two opposing ideas in mind at the same time and still retain the ability to function. One should, for example, be able to see that things are hopeless yet be determined to make them otherwise.

Farnam Street adds:

“Any year that passes in which you don’t destroy one of your best loved ideas is a wasted year,” says Charlie Munger. If only it were that easy. It’s mentally hard to come to an opinion and even harder to give up that attachment and admit that we were wrong. That’s one reason Henry Singleton opted for flexibility instead of predetermined plans.

Great line by Bill Murray:

You need all kinds of influences, including negative ones, to challenge what you believe in.