Keep enough forward motion that doubt has to chase you.

Doubt does its best work in stillness. When nothing is happening, there is plenty of room to reconsider everything, question whether you are suited to this, and construct reasons to stop. When you are moving, the same doubts still exist and have to keep up, and they tend to be less persuasive alongside evidence that the thing is progressing.

On a day full of doubt, try acting before resolving it. Do the smallest piece of the work and see how the doubt sounds afterwards. This is not a way to silence it, only to stop giving it an empty room to speak in.