overconfident
/ˌoʊvərˈkɑnfɪdənt/
adjective
- Having too much belief in one's own abilities, knowledge, or chances of success, often leading to mistakes.
- He was overconfident about passing the test without studying, so he failed.
- The team's overconfident attitude caused them to underestimate their opponents.
- Being overconfident can make you ignore important warnings.