The Green Lantern Corps are among the most powerful intergalactic peacekeeping force in the entire DC Universe. By tapping into the Power Battery on the planet Oa, the Green Lanterns can use their power rings to materialize any object they can imagine, so far as their willpower and courage remains strong. And while the power ring is one of the most powerful and seemingly impervious tools in the universe, it is not without its limitations. Sometimes those limitations and weaknesses can have dire consequences, as Green Lantern John Stewart once learned the hard way.
During the second issue of the Cosmic Odyssey event, the cosmic being Metron, upon learning the Anti-Life Equation, has been rendered comatose after his mind was shattered from the knowledge. The Anti-Life Equation, having been rendered into a living entity after using Metron's mind to escape its reality, splits itself into four pieces (Anti-Life Aspects), which then land on four separate planets (Earth, Thanagar, Xanshi, and Rann). Unable to contain the power within, Darkseid forms an alliance with Highfather, and calls on some of Earth's most powerful heroes to help track down and contain the Aspects. If any two of the four planets manage to be destroyed by the Aspects, it will start a chain reaction that would destroy the galaxy.
While Superman and Orion, son of Darkseid, arrive on Thanagar, and Lightray and Starfire search Rann for Adam Strange, the inhabitants of both planets rage separately: the Thanagarians attack the two heroes; while on Rann, the populace has been driven violently insane. On Xanshi, Green Lantern John Stewart, and the Martian Manhunter find the populace stricken by a debilitating plague. Rendering a quick remedy from which a local doctor attempts to derive a serum, the two heroes track an energy signature to a weather station on the planet's arctic poles. The station has been taken under control by the Aspect, as it attacks Martian Manhunter and Green Lantern with lightning and gale-force winds. Hoping to avoid being slowed down trying to protect his companion, Green Lantern encases Martian Manhunter within a protective case conjured by his power ring, and rushes off on his own.
In a classic case of being too stubborn for his own good, John Stewart rushes into the weather control station, prepared to capture the Aspect and save the planet...only to realize the entire interior of the station, and the Aspect itself, has been painted yellow, the one color over which his ring is useless. As he watches helplessly, and as Martian Manhunter watches from a distance, the weather control station overloads, detonating itself, and the Aspect with it, which results in the entire planet of Xanshi slowly exploding in half, and then blowing itself out of its own orbit, and into its sun, which then destructs in an incredible manner. Despite being one of the best and esteemed members of the Green Lantern Corps, this proved a job much to big for him to handle alone.
The fallout of Green Lantern's disastrous handling of the Aspect leads Martian Manhunter to berate him for his arrogance, saying, "Thanks to your arrogance and stupidity, I have now seen two worlds die. I will never forgive you for this." It is less important that the Aspect had been painted yellow (one of the few weak points for the Power Rings), and more important that John Stewart's independent streak and rigid personality was too strong to overcome. It is perhaps the greatest failure of John Stewart, and one that doomed not only billions, but threatened to doom the entire galaxy. Partnering up and asking for a helping hand proved a bit too much for this Green Lantern, and in the end it cost countless lives.