“Who once has doubted never quite believes.”

“One never quite stops believing, some doubt remains forever".”

“Who never doubted never half believed
Where doubt there truth is—'t is her shadow.”

“I had never doubted my own abilities, but I was quite prepared to believe that "the world" would decline to recognize them.”

“If you quit ONCE it becomes a habit. Never quit!!!”

“Believe those who seek the truth, doubt those who find it; doubt all, but do not doubt yourself.”

“I've never quite believed that one chance is all I get”

“It would be so foolish of you to form a team that has many people who doubt, rather than having true believers in your cause.”

“Aristotle’s view that philosophy begins with wonder, not as in our day with doubt, is a positive point of departure for philosophy. Indeed, the world will no doubt learn that it does not do to begin with the negative, and the reason for success up to the present is that philosophers have never quite surrendered to the negative and thus have never earnestly done what they have said. They merely flirt with doubt.”

“Do not doubt him who tells you he is afraid, but be afraid of him who tells you he has no doubts.”