Most fictional characters are walking archetypes dressed in specific clothes. The difference between a character and a person is contradiction — and learning to write it changes everything.
Every writing workshop in the world will tell you: give your characters wants, needs, and flaws. This is correct and almost entirely useless advice, because wanting something and needing something and having flaws is what defines a character in theory. What makes a character feel real in practice is something harder to teach: contradiction.
Real people contain multitudes that don't resolve neatly. The generous man who resents the people he helps. The brave woman who is terrified of intimacy. The brilliant thinker who makes catastrophically bad choices about love. These contradictions aren't flaws in the person — they are the person. Writing characters who contain unresolved contradictions is writing people.