It is a psychological effect in which people don't realize their level of knowledge or ability in a subject. People who know little about a subject will think that they know more than they actually know. People of low ability may not have enough intelligence to fully grasp how complicated something can be, causing them to overestimate their knowledge or ability. This can cause them to underestimate the intelligence of a high ability person who claims something is complicated when they falsely believe they understand it fully. 