Enthusiast for self-improvement appears to be happy (6)

I believe the answer is:
smiles
I'm afraid I can't explain this answer.
Can you help me to learn more?
(Other definitions for smiles that I've seen before include "Looks happy" , "Facial expressions showing pleasure" , "Shows signs of pleasure or amusement" , "Gives visible sign of pleasure" , "Beams, grins" .)
