To underestimate oneself is as much an exaggeration of one's powers than the other.

We underestimate the value of what each one of us can do.

We tend to underestimate the small things about ourselves that are often our most valuable attributes.

...to underestimate one’s self is as much a departure from truth as to exaggerate one’s own powers.

We seem to be unable to resist overstating every aspect of ourselves: how long we are on the planet for, how much it matters what we achieve, how rare and unfair are our professional failures, how rife with misunderstandings are our relationships, how deep are our sorrows. Melodrama is individually always the order of the day.

[Y]et I think that we are inclined to under-estimate our own powers [...] and to exaggerate the importance of the Jewish influence. Hand in hand with this goes the perfectly ridiculous and revolting tendency to make the Jews the general scapegoat for all the vices of our time...

The truth is, we often underestimate by as much as 50 percent how much others are willing to help us when asked. As we talked about in chapter 2, being mistrustful or assuming others are selfish can be self-fulfilling prophecies.

In hundreds of studies, researchers have consistently found that we overestimate our own attractiveness, intelligence, work ethic, chances for success

We underestimate the distance between ourselves and others. Not just inferential distance, but distances of temperament and ability, distances of situation and resource, distances of unspoken knowledge and unnoticed skills and luck, distances of interior landscape.

I'm constantly amazed by how easily we love ourselves above all others, yet we put more stock in the opinions of others than in our own estimation of self....How much credence we give to the opinions our peers have of us and how little to our very own!

It is also true that the less competent a person is in a given domain, the more he will tend to overestimate his abilities. This often produces an ugly marriage of confidence and ignorance that is very difficult to correct for.

41 Never exaggerate. It isn’t wise to use superlatives. They offend the truth and cast doubt on your judgment. By exaggerating, you squander your praise and reveal a lack of knowledge and taste. Praise awakens curiosity, which begets desire, and later, when the goods seem overpriced, as often happens, expectation feels cheated and avenges itself by running down the praised and the praiser. The prudent show restraint, and would rather fall short than long. True eminences are rare, so temper your esteem. To overvalue something is a form of lying. It can ruin your reputation for good taste, and — even worse — for wisdom.

People tend to underestimate him on first acquaintance. It’s a mistake they only make once. Whether or not they survive.

When someone is viewed as more extraordinary than they are, you're more likely to overvalue their opinion on things they have no special talent in. Like a successful hedge fund manager's political views, or a politician's investment advice.