Appeal to confidence

You're going to like the way you look. I guarantee it.

An appeal to confidence occurs when somebody's confidence in some fact is taken as proof of that fact. On the other hand, an appeal to unconfidence (also ad fidentia, against self-confidence) occurs when somebody's lack of confidence in some fact is taken as disproof of that fact. Either appeal ties confidence to authority and ties authority to truth.

It is an appeal to authority (or lack of authority), an informal fallacy, and a fallacious argument.

If the arguer additionally states something along the lines of "doesn't his confidence just lift your spirits?" or the inverse, it also qualifies as an emotional appeal.

Of note, it is related to the Dunning–Kruger effect.

Form
Appeal to confidence:

Or:

Appeal to unconfidence:

Or: