The Saturday Night Live character Stuart Smalley may be one of television's least-assured humans. Mr Smalley's "Daily Affirmation" comedy skit pokes fun at those who question being "good enough" or "smart enough"; it's satirical confidence building - from a guy in silly sweaters.
American television may make a mockery of self-doubt, but it turns out that Mr Smalley does not suffer from uncertainty on his own.
A group of scientists from the United States have revealed that macaques - a type of Old World monkey - can doubt themselves, too.
Using a computer simulator researchers taught the primates to guess at the density of a pixelated screen. When the monkeys answered correctly they were rewarded with food. Wrong answers brought no food, and a delay in play.
If the monkeys did not know the answer, however, they could choose to "pass" rather than guess incorrectly. This brought no food but no delay either, meaning less time before the next correct answer.
Researchers reason that the monkey's ability to question itself proves that they, like humans, "know when they don't know". This skill, says David Smith of the State University of New York at Buffalo, is "one of the most important facets of humans' reflective mind".
Self-doubt is not usually so rewarding. But monkeys everywhere should take solace: confidence can indeed be learnt. Al Franken, who played the sweater-wearing psychologist on TV, certainly knew this. Today, he's in the US Senate, where a monkey's gift of being able to admit ignorance can often be in short supply.