It’s a human frailty to see in others what we want to see, rather than what is. This works both ways – sometimes we idolize someone undeserving and sometimes we find intention when there is only human error.
We also project our own fears and weaknesses onto others. Our dislike of someone confident says more about our own self-esteem than it does their alleged arrogance. When someone criticizes another’s physical appearance, you can bet that person is equally critical of what they see in the mirror.
The personas we adopt also play a part. As writers, it’s tempting to see every person we meet as a potential reader. If you’re the class clown, the people around you are your audience. They may not wish to be, but that’s what you see.
What does your protagonist project onto the other characters in your novel? What weaknesses do they loath in others? Do they resent another person’s excellence? When they enter a room, do they see people to amuse or impress? Do they see customers or competitors?
How your protagonist views the other people in his story world and what he likes or dislikes about them says volumes about his character. Take a look at a current or recent project and consider what your character is actually saying when he talks about someone else.