You know that book you love? Remember that evil character in it that you really despise? Do they think they are the bad character? No. They do not see themselves as the heartless tyrant, the slinking coward, the greedy manipulator, the guilt-ridden critic, or even the plucky sidekick. Everyone is the HERO of their own story!
No one has an objective view of their own narrative. When you analyze your own story, be sure to do it honestly. Maybe you are the plucky sidekick. What’s wrong with that? Everyone loves that character! Just be sure you’re not those other characters who think they are noble or brave with a “high and lonely calling,” but everyone reading the story properly can see that they are just the pits! Don’t be that one.
Likewise, when creating a story, your antagonist should not be aware that they are wicked. They need to think they are in someway righteous, doing what they do for “the greater good” and believing that the end justifies the means. Those are the most evil (and believable) characters. A sliver of truth deceiving them into believing the lie that they are virtuous.
Also, don’t be that character.