It's everything for some; nothing for others (4)
I believe the answer is:
love
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for love that I've seen before include "Score of zero at tennis" , "All you need, according to the song" , "Precious" , "God of 20 Dn" , "Serenade" .)