Actually I'm not sure if I must have mercy for that stupid or I have to review my self confidence again.
Everybody look like they have a high opinion about themselves and those opinions are all true only if human intelligence is unique in each person and if it's incomparable with other intelligence.
Supposing we are all more intelligent than others, we must all have some superior brain skills that differentiate us from each other.
Actually this is a fact, that's why we think we are smarter than our peers when we compare ourselves with them.
But if this is true for all of us, why we must be less intelligent than others at the same time?
Yes we are stupids too, at least in some areas we lack skills and abilities but we don't give any high importance to the skills we lack,
so all these opinions are different because we measure things we want to measure and undervalue others.
Sometimes a person might believe he is more intelligent than others because of his beliefs.
When someone believes blindly the knowledge he has, he might feel himself smarter than others because he thinks he knows something important that others don't know,
but make him doubt that knowledge and you'll see him doubt his intelligence.
Intelligence is a subject of many prejudices, because appearance, the way you talk, etc can highly affect opinions. (Read How to appear very intelligent)