The phrase "sure of oneself" implies a high level of confidence in one's abilities or opinions. Its antonyms can range from self-doubt to humility, with several shades in between. The opposite of being sure of oneself can be described as uncertain, hesitant, unconfident, or diffident. It can also mean having a lack of clarity or a confused state of mind. On the other hand, being open-minded, receptive, or even modest and self-effacing can be deemed as a contrasting approach to being excessively sure of oneself. Nonetheless, in the right measure, being confident and self-assured can be a useful trait, but not when it leads to arrogance or intolerance.