What makes someone develop a superiority complex?

I made a similar post a few hours ago, but it was bloated with unnecessary details and a general lack of focus. I've since deleted it, and I'm making this now that I've time to think about what I want to ask.

I'm making a scientist character, with genuinely good intentions, but an attitude that makes them almost impossible to work with. They have a severe superiority complex, and an unwillingness to trust in the competence of anyone other than himself.

Thing is that I don't really know anything about the psychology behind a superiority complex. Short-term arrogance is one thing, but I'm not sure what factors bring about such a complex in the long-term. I was hoping someone more familiar or at least informed on the topic than me could shed some light on what might make a character develop a superiority complex?