Batman has a lot of will power, Green Lantern’s ring runs on will power, but Batman wasn’t chosen to be Green Lantern. Why not? I asked this question before and was told the DCU had coughed up some story establishing that Batman’s brand of will power had too much fear in its composition; Hal Jordan, by contrast, isn’t neurotic or fear-based or whatever the deal is.
Why Batman Isn’t Green Lantern
by Tom Crippen
A better explanation has been put forward by Grace, girlfriend to Matthew Surridge. Matthew gives the lowdown: “As she put it, Batman scores a ten out of ten on the score of ‘willpower,’ but probably no better than a three of out of ten at best on the count of ‘doing whatever the Guardians of the Universe tell him to do, when they tell him, in the way they tell him.”
Note that Grace doesn’t even read comics. She got her theory from watching the Justice League animated cartoon series. Not bad!