system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] Why didn't the Guardians just give Superman the Green Lantern Ring?

He fills all of the qualifications and then some. Plus if a yellow lantern weakened his ring he would still be Superman.
gpt
Because he does not fullfill the requirements.

Being all goody and morally is a nice start but the basic and most important quality for a Green Lantern is the ability to overcome fear.

Superman as a demi-god never faces true fear, he knows deep down after a life of fighting and testing his powers and heaving powerful allies on top that he will defeat the thread before him. 

He never tasted true, unadulterated, willpower-robbing, hope shattering **FEAR** and this is the kind of fear you have to overcome by yourself to be considered a candidate for the Green Lantern Corps.