The illusion of asymmetric insight is a cognitive bias whereby people perceive their knowledge of others to surpass other people’s knowledge of themselves. This bias seems to be due to the conviction that observed behaviors are more revealing of others than self, while private thoughts and feelings are more revealing of the self.
We commonly believe that we understand others better than they understand us. The rationale for this stems from our external, objective viewpoint and the assumption that the other person has a significant blind self, whilst our own blind self is small.
There is also asymmetry in the reverse situation — we believe we understand ourselves better than others understand us and may feel insulted if they try to show they understand us more than we do.
The same effect happens for groups, where the in-group believes they understand out-groups better than out-groups understand them.
Overall, this is a position where we generally assume we know more than others, perhaps because we know more about what we know.
In an argument with another person you tell them what they are like in great detail because clearly they have very little self-knowledge. They argue back telling you things about yourself that are clearly wrong or that you knew anyway. How can people be so stupid?