Absolutely not true. I don't have certainty about anything, but I do want a reason to consider a thing, and I will absolutely weigh something on its merits, and on its probability. If I were to believe anything anyone said to me, with no evidence to support its being true, then I would necessarily be convinced of all manner of contradicting absurdities. If not evidence, what reason would I have to differentiate between these things?
Rationality will only get you to probability. Personal commitment will get you to certainty.