While Goku may wield divine power, there is one person who has existed throughout Dragon Ball legend who he will never be able to defeat.
Few people in the Dragon Ball universe have defeated Goku, and with enough time and effort, he will most likely be able to defeat them in the future — yet Dragon Ball Super affirms that there is one person Goku will never be able to defeat, no matter how much training he receives.
Goku is one of the most powerful fighters in the universe, and his power has increased enormously in Dragon Ball's recent history, from that of a previously established Saiyan warrior to that of a true deity. During the Tournament of Might in Dragon Ball Super, Goku battles a warrior named Jiren whose power surpasses that of his God of Destruction. Goku was able to access the angelic power of Ultra Instinct while fighting Jiren, which signified a new level of power for him that he had never even come close to achieving before. Ultra Instinct is Goku's most powerful form yet, capable of defeating any Super Saiyan form, and it was enough to send Jiren on the road to defeat, yet it wouldn't matter against the one person Goku will always lose to.
Frieza can never use his most powerful attack in Dragon Ball Super.
After the events of Dragon Ball Z, which culminated with Goku and the others finally beating the wicked Buu, Goku and the rest of the Z Fighters are taking a much-needed rest in Dragon Ball Super Chapter 1 by Akira Toriyama and Toyotarou. Despite the fact that all threats to Earth have been eradicated (for the time being), Goku is in an arguably worse situation: finding work. In this issue, it appears that Goku has found a stable job that pays the bills but drains his soul and requires him to spend his days doing meaningless work for money rather than training. Chi-Chi, on the other hand, is a better worker than Goku. Goku tells his kid, Goten, that he wishes he could just stop and train with King Kai, but that he won't because his wife, Chi-Chi, would be happy. Goten responds, "In that sense, she's the strongest woman in the universe," a remark that they both laughed heartily at, despite the fact that they both knew it wasn't a joke.
Goku can channel angelic power and go toe-to-toe with genuine gods, even becoming a deity in the process, but he'll never be able to defeat Chi-Chi. Chi-Chi is always there to correct Goku when he goes too far in his training or comes dangerously close to missing significant milestones in his boys' lives, and he typically listens because he wouldn't dare to oppose her. Goku isn't alone in this regard; Vegeta has a similar connection with Bulma, albeit Vegeta has a far bigger tantrum when she asks him to do something he doesn't want to do (like when the whole family went on vacation in Dragon Ball Super, for instance). This isn't an accident, as heterosexual Saiyan men are more attracted to women who take charge in the relationship, as revealed in a later chapter.
While Goku could certainly annihilate Chi-Chi in hand-to-hand battle, he wouldn't dare to lift a finger to her for fear of what he would face if he did, and that is true power. Chi-Chi is the one person Goku could never defeat, since she would just lecture him into submission and finish the 'battle' before it had started, according to Dragon Ball Super.