When it came to the backstory of the Green Lantern Corps, one point was often mentioned: Green Lanterns feared Yellow Lantern energy.
Logically speaking, although the Lantern Corps came in different colors, it was not like in online games where attributes countered one another. The various Corps were basically equal, merely representing different emotions, which was why their colors differed. There was no reason one had to restrain another, so why were Green Lanterns weak against yellow?
That had to start with those unfortunate little blue men.
As the first Intelligent Life to emerge in the universe, and a super-civilization that had developed for countless tens of thousands of years, after using the Emotional Spectrum of the universe to create the Green Lantern Corps, they naturally worried, like any other intelligent civilization, that the Corps they had created would rebel against them.
Then this incomparably powerful race came up with a brilliant idea to prevent the Green Lantern Corps from betraying them: they stuffed Parallax, the Yellow Lantern Beast representing fear, into the Green Lantern Corps' Central Power Battery.
The Green Lantern Central Power Battery could seal Parallax, but at the same time, the Yellow Lantern Beast Parallax had invaded it, becoming a blind spot in the Green Lantern spectrum. Thus, Yellow Lantern energy became the Green Lanterns' weakness. Once they encountered that energy, they would lose all combat ability at best and become severely weakened at worst.
Then the little blue men painted their own houses yellow, figuring that Green Lanterns would not dare attack them.
This powerful race born in the early days of the universe, these immensely advanced super-beings, did not adopt any of the measures Intelligent Life should have used to prevent their creations from rebelling—planning systems, class separation, supporting rulers, and so on. Instead, after