Being self-confident is a little like having a unicorn. Everyone wants one, it’s very hard to find, and if you have too many unicorns, or too much self confidence, we all want you to shut up about it already.
Everyone has areas in which they are extremely self-confident. For example, I’m very good at making absurd noises when startled and developing Wikipedia-induced paranoia. If we were measuring my confidence in unicorns, I would have several herds when it comes to these specialities. (According to the Internet, a group of unicorns is called a “blessing”. The reason for this is that unicorns are cocky.)