Dragon Ball as a story doesn't fail to present the strengths and weaknesses of almost all of his characters, and for the most part it succeeds in that regard. Vegeta, Frieza, and even Beerus all seem to have weaknesses that re completely obvious and usually easily exploitable in their own way. Vegeta's pride has been his Achilles heel, and even Frieza's arrogance and tendency to underestimate his opponents has led him to being blindsided by Son Goku. One would be forgiven if they were to think that would make Goku almost perfect and completely devoid of any weaknesses or even exploitable defenses, but the simple truth is that even the strongest fighter in the show himself has an exploitable weakness. The only thing is, that it may not be obvious at first or what Dragon Ball Super wants you to think. The truth being, that his weakness happens to be something that has plagued Goku ever since his early young years.
Son Goku as a fighter is exceptionally hard-working, as opposed to talented in any sense of the word. One need only look at his early years during the Dragon Ball run, where he learned from various Masters the value of working hard and trying to become stronger through your own efforts despite the difficulties. Eventually, as Dragon Ball Z and Dragon Ball Super went on, Goku achieved new transformations and a myriad of techniques he learned and expanded on. However, many fans seem to be misunderstanding this immense growth as perfection or due to his lack of any weaknesses. Whether it be true or a falsehood, Goku's progress is filled with its own struggles and the one weakness that Goku as a child had, and still has even as a grown adult in some ways. Just what this weakness is depends on who you ask, but it is a hot topic of debate to many fans of Dragon Ball for good reason.
Goku's Learning Style
While Goku has learned various techniques and has grown through hard work and dedication, his learning style happens to be the major weakness that actually is what's holding Goku back on an infinitesimal amount, but is major. Ever since his tutelage under Master Roshi, even Son Goku didn't understand many concepts that are based on being a visual learner as opposed to being an action learner; Goku doesn't really delve deep into how every technique works on a technical level. Even down to his most infamous technique, the Kamehameha, Goku wouldn't be able to tell you the technical faculties of being able to use the Kamehameha unless he tried it himself. He's more of an action learner, meaning that Goku would need a simple explanation of the technique and what it does for him to understand it and quickly apply it into his own fighting style.
Even with the use of techniques like the Solar Flare, Instant Transmission, and eventually the Kaioken and Spirit Bomb; Son Goku always had to exert himself to learn the techniques not on a technical level but on a practical level. In that way, Goku's ability to learn is only hampered by so much as his ability to understand the simple concept of thew technique and applying it with enough practice. Despite his initial ability to use the Kamehameha technique as instructed by Master Roshi, eventually it took more practice and a lot more application to create more destructive and powerful Kamehameha's that are torrential in energy. Even with the knowledge of the Solar Flare, or techniques like Instant Transmission; it is most likely the simplicity of these abilities is what allowed Goku to learn them at a faster pace then usual.
A Weakness That's Important.
Despite its seemingly small role in Goku's development as a fighter and main protagonist, the fact that his learning capabilities are not as fast or even visual as opposed to many combatants in Dragon Ball, makes his weakness much more grounded and allows the audience to find ways to connect with Goku. After all, not everybody can be such a quick learner or talented like many others, but many can relate and be inspired by a hard worker who understands the world in a simplistic but deep viewpoint, never stopping his self-improvement. Many fans may find this piece of news refreshing, and even agreeable that Goku's weakness of slow-learning makes for a more relatable and grounded way of explaining most of his character flaws as well as some moments of comedy.
Of course, the chance of a disagreement within the fans is also possible. As stated before, Goku's one true weakness may be his learning capabilities, but there are various other debatable weaknesses that many are willing to provide examples for. Overall, understanding Goku's weaknesses is not an exercise in futility but an exercise in discussion and analysis of Goku's strengths and the times he was caught off guard. However, whether Goku's weakness may be his naivety or his slow-learning, the fact remains that Son Goku as a character will become as relatable and inspiring to many fans of Dragon Ball. Ever since the beginning, the story has been able to present Goku in a positive inspiring light.