In the Marvel Cinematic Universe, the Infinity Stones are treated with a heavy degree of importance as they represent the core foundations that started the universe. As a result, they carry immense power both scientifically and spiritually. The full range of these stones was showcased throughout The Infinity Saga, from putting out massive amounts of radiation to even having mystical properties. But when together, they’re nearly impossible to wield. That said, why could Thanos perform this feat without succumbing to its negative effects before he snapped?
In the comics, Thanos is an Eternal with a Deviant gene. This was why he looked different from other Eternals and also carried immense strength and other powerful properties. However, in the MCU, aside from being a brother to Starfox, his heritage has yet to be fully explored. Therefore, it’s more likely that he was simply a part of a race from Titan and possibly stronger than his peers. But that alone couldn’t be enough to weather the immense energy put out by the stones. To do that, Thanos had to put in work that was both necessary to his goal and incredibly violent.
When the Hulk tried to use the stones, the Gamma Radiation severely damaged his arm, and the snap made it all but useless. Considering he’s the only being that could physically stand up to The Mad Titan, it proved just how deadly the gauntlet could be. But for Thanos, his intellect matched or even surpassed his strength, and he knew that he would need to be physically prepared for his journey. To do this, he must’ve devoted himself to being in peak physical condition in the worst way imaginable.
Over the years, Thanos used his belief in universal balance to motivate him. With each planet, he grew stronger both in power and resolve. Once the time came for him to wield the stones, he knew that the endless war had honed his mind and body to endure their effects. He also likely researched each stone and its effects, readying himself through battle. As a result, the army he brought with him to each planet was likely just a scare tactic, as he could’ve decimated an entire empire on his own if he wanted to.
The MCU’s Black Order may have also played a part in his training since they each had skills and abilities that could help him train to control the stones. For example, Ebony Maw used telekinesis, which meant that Thanos’ mind had to be immensely strong to withstand the Maw’s attacks physically. Meanwhile, fighting Cull Obsidian would have given Thanos the strength he needed to fend off the Power Stone’s energy. Proxima Midnight and Corvus Glaive could’ve attuned Thanos’ mind and reflexes so that he could counter each stone as they overtook his body.
For years, Thanos was built up to be one of the strongest and deadliest enemies in the MCU, and that fear was completely justified. Through research and bloody conquest, Thanos likely used his skills to hold back the Infinity Stones’ desire to rip him apart atom by atom before The Snap. So, in the end, it was no surprise that it took cunning and a heroic sacrifice to beat an enemy who had molded himself to be the sole user of the Infinity Gauntlet.