While Goku is one of the strongest beings in the Dragon Ball universe, no one ever said he was smart, and in one instance, Goku proves he’s too dumb to realize the one way he’s weaker than Superman, and nearly gets himself killed in the process. Goku and Superman have very similar origin stories and are both incredibly powerful heroes in their respective universes. However, Superman has one huge advantage over Goku, one that Goku didn’t realize until it was almost too late.
In Dragon Ball Super Chapter 49 by Akira Toriyama and Toyotarou, the planet-eating sorcerer Moro has launched a full assault against New Namek and the heroes that are trying to protect the planet and its people. Goku and Vegeta are doing their best to battle the foe, but Moro’s ability to drain them of their power is keeping them from using their full strength. Eventually, Moro grows tired of battling the Saiyans and flies into space where he planned on waiting for his reinforcements to arrive.
When Moro flew into space, Goku chased after him as the Z-Fighter was determined to put a stop to his reign of villainy before it truly began. However, before Goku got too far off-world, Vegeta stopped him by reminding him of one crucial detail about Saiyan biology. Saiyans cannot survive in the vacuum of space, a fact Goku knew but was too dumb to consider while he blindly ran after his target. If Vegeta hadn’t stopped him, Goku would have died a pretty underwhelming death considering he has fought in a multiversal tournament and has gone toe-to-toe with gods.
While Goku and the other Saiyans cannot naturally survive in space, Superman has no problem flying through the cosmos while in the light of a yellow sun. Superman’s powers make him virtually immortal with no need for food, water, or oxygen to survive and his one weakness is Kryptonite. A Saiyan is much more mortal by comparison as they can be killed in battle, need sustenance to survive, and can’t fly around in space.
Even though a Saiyan doesn’t have all of the same perks as a Kryptonian under a yellow sun, the potential for how powerful they can become is nearly unparalleled. Goku and Vegeta have each been able to access the power of gods and angels in recent Dragon Ball storylines, transcending previous notions for how strong a Saiyan can become. However, after Goku was weakened in his fight with Moro, he forgot the one way he is weaker than Superman, and it nearly got him killed.