Bandura held that the most powerful source of self-efficacy is mastery experience - actually succeeding at the task - well ahead of encouragement from others. Why would being told you can do it work so much less well?

D. Because performing the task is direct evidence about capability.

Doing the thing is the most direct evidence available about your own capability; being told you can is evidence about someone else's estimate, mediated by whether they are being kind. Encouragement unsupported by experience is overturned by the first genuine failure, which is why graded exposure and scaffolded instruction start absurdly easy on purpose.