Why do people who are capable say that they can't, but in fact, they are better?

The more capable people are, the more they will value others' opinions about themselves, so they will leave a good impression on others, and they will not show too much if they don't keep up with the competition and keep a low profile. The less capable people will be afraid that others will say that they are incompetent, so they will "brag" and exaggerate themselves. They just want to prove themselves in front of others, but they are a bit overdone and unreal, which is an immature performance.