Indomitable Will

From Green Lantern Wiki

Often a prerequisite of joining the Green Lantern Corps, an indomitable will makes happens when a person has unmovable beliefs or has incredible willpower. This willpower allows them to easily control their emotions. In the case of a Green Lantern Corps member, it allows them to utilize their rings without much effort. In the case of Batman, because of his indomitable will and previous use of a Power Ring, he was able to reject a Qwardian Power Ring that tried to recruit him into the Sinestro Corps.