Είμαι βέβαιος για την επιτυχία σου.

English Translation

I’m sure of your success.

βέβαιος: This is an adjective meaning “certain” or “sure.” It agrees in gender (masculine), number (singular), and case (nominative) with the subject of the sentence, which is implied to be a male speaker. If the speaker were female, the word would change to “βέβαιη.”