If you are incautious, you do not stop and think about what might go wrong. It lives next to careless and reckless, but they are not twins. Careless often means you did not pay attention; reckless is hotter — you saw the danger and still charged in; incautious is a more formal, slightly old-fashioned word for not being careful enough, not looking ahead. You are more likely to meet it in writing than in the corridor. A person, a remark, or a move can be incautious. The opposite is cautious.