You ask, "What is doubt?"
Doubt is the belief that what you intend to create will not manifest.
And yet, it is the belief itself that creates the manifestation of this illusion.
Do you follow me?
The very act of doubting creates the result of not receiving, proving once again that you, yourSelf, created it.
Sometimes, you doubt something and still it manifests. You do this to further the illusion.
Beneath the doubt is the belief that you can doubt and still receive; that Life is chance, luck, fate.
You believe this, and therefore you experience it.
You can choose FAITH or DOUBT, but FAITH feels a lot better.