It's a VERY popular archetype. Manga and anime are flooded with characters who just aren't positive if they can...ace that test, take that new job, propose to that person...and do anyway.
Yuri from Yuri on Ice!!! is a great example. He is shy (except when he is drinking), gets nervous, doubts himself and doesn't live up to his potential.
However, hints that Yuri is tougher than he thinks are there from the beginning; they aren't tacked on to allow for a great moment. His friends tell Victor, his coach and partner, that Yuri is a "sore loser." In the context, they are confirming for Victor that Yuri doesn't like to lose--and the fact is, nobody makes it to "Nationals" in the skating world without being competitive.
Yuri doesn't want to give up, no matter how often he berates himself. His personality being what it is, he needs someone to skate FOR, and Victor supplies that motivation. But his decision to throw himself completely into a routine is all Yuri. At one point, Victor--who is taking a break from skating to be a coach and is not entirely sure how to distill confidence in his skater--tries a kind of reverse psychology to shake Yuri up. It works, but only because Yuri thinks Victor is behaving like a flake. The inherent toughness of Yuri, which has always been there, comes to the fore. He pushes himself on the ice and excels. All the skaters, of course, are very, very good (I remember watching the Olympics once where a male runner trailed in several seconds behind everyone else--and I realized that by anyone else's reckoning, that male runner was still faster than most people). The series does an excellent job underscoring the desire to get ahead even within placid, good-humored skaters. Yuri is not as inherently talented as Yurio, his rival (his rival from Yurio's point of view, at least), but he is talented, has tremendous stamina and the ability to persevere. He also has the maturity to pull together his act, a fact that Yurio recognizes early on. Yuri may come off as adorably self-effacing. He knows what he wants.Other laid-back action heroes:
- Karasuma from Assassination Classroom
- Justin from Secret of Nimh
- Sam Gillespie from Sister Boniface
- Lieutenant Tao from Major Crimes
- Itami from Gate