Logical person sure to succeed (7)
I believe the answer is:
natural
'logical' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for natural that I've seen before include "Not synthetic or man-made" , "Not artificial; off-white" , "as one might expect" , "Simpleton" , "Innate, inborn" .)