sure of oneself

/SH UH1 R AH0 V W AH0 N S EH0 L F/
adjective
  1. 1

    Self-confident.

    โ€œWhen it came to sport, he was really sure of himself: he knew he was good.โ€

Source: https://en.wiktionary.org/wiki/sure%20of%20oneself