To win only subsequently leads to optimism seen in an individual (2,3,4)
I believe the answer is:
on the nose
'to win only' is the definition.
(term when betting on horseracing)
I don't understand the rest of the clue.
(Other definitions for on the nose that I've seen before include "characteristic of glasses?" , "where glasses are found?" , "To win one" , "Exactly in America" , "where glasses rest" .)