overconfidence
Having too much confidence, so you make avoidable mistakes.
Overconfidence is having too much belief in your own abilities or knowledge, to the point where it leads you astray. It's different from regular confidence, which helps you try new things. Overconfidence makes you think you're better prepared than you actually are, and it often leads to mistakes you could have avoided.
An overconfident student might skip studying for a spelling test, certain they already know all the words, then get surprised by a low grade. An overconfident chess player might ignore their opponent's strategy because they're so sure they'll win, only to get checkmated. In both cases, a little honest self-assessment would have helped.
Overconfidence is especially tricky because it feels good. When you're overconfident, you don't feel worried or uncertain at all. You feel great! That's why it can sneak up on people. Skilled experts in any field often stay humble because they understand how much there is still to learn.
You can spot overconfidence in yourself by paying attention to that moment when you think this will be easy or I don't need to prepare for this. Those thoughts might be true, but they might also be overconfidence talking. Careful people double-check themselves, practice even when they think they're ready, and stay open to the possibility that they might be wrong.