Certain
Part of speech: determiner
Definition: Having been determined but unspecified. The quality of some particular subject or object which is known by the speaker to have been specifically singled out among similar entities of its class.
Part of speech: adjective
Definition: Sure, positive, not doubting.
Example sentence: I spent a lot of years trying to outrun or outsmart vulnerability by making things certain and definite, black and white, good and bad. My inability to lean into the discomfort of vulnerability limited the fullness of those important experiences that are wrought with uncertainty: Love, belonging, trust, joy, and creativity to name a few.
Sure
Part of speech: adjective
Definition: Physically secure and certain, non-failing, reliable.Certain in one's knowledge or belief.
Part of speech: interjection
Definition: Yes, of course.
Example sentence: I'm selfish, impatient, and a little insecure. I make mistakes, I'm out of control, and at times hard to handle. But if you can't handle me at my worst, then you sure as hell don't deserve me at my best.