sure of (oneself)
Very self-confident. You can't go into that interview wondering if you're good enough for the job—if you're sure of yourself, the interviewer will be sure of you, too. A: "Well, Tammy's very sure of himself, isn't she?" B: "Yeah, we've never needed to worry about her succeeding in life."
sure of oneself
Self-confident, as in Now that Mary's graduated she's much more sure of herself. This expression uses sure in the sense of "confident" or "secure," a usage dating from the mid-1400s.
ˈsure of yourself
(sometimes disapproving) very confident: She seems very sure of herself.