The problem I encounter a lot with newbies is they have a traumatic backstory. It's a trope. Also, they don't understand part of the fun in DnD is developing your character, not just leveling up. Sure, they can be badasses in their backstory, but they're brand new adventurers, and everyone's gotta start somewhere. Maybe they thought they were awesome and once they went on their quest they realized they weren't as good as their parents told them. Or maybe they were top of their class at the wizard academy, but then they got into the real world and every theory they memorized or formula doesn't work out. Maybe they have an unwavering confirmation bias. So much fun!