Psychology says people who always underestimate others aren't necessarily confident: What this behavior reveals?

Psychology says people who always underestimate others aren't always confident in their own abilities. This behavior can be linked to insecurity, low self-worth, ego defense, comparison and fear of competition. Psychology theories such as the Dunning-Kruger Effect and Alfred Adler's ideas about inferiority can help explain why some people reduce the abilities of others to protect their own sense of worth.