An episode of Dragon Ball Super makes a huge change to the original Super Saiyan transformation by providing a whole new explanation for how it works. Since it was first discovered by Goku in the Frieza Saga, the Super Saiyan form has been surpassed by a number of more powerful variations, such as Super Saiyan 2, Super Saiyan God, Super Saiyan Blue, and the non-canon Super Saiyan 4. But whereas once-impressive transformations like Super Saiyan 3 have become irrelevant over time, the original Super Saiyan form has remained consistently important.
The first-ever Super Saiyan transformation remains one of the most memorable and iconic moments in the history of the anime. Though the phase "Super Saiyan" had been uttered often, exactly what it meant was left ambiguous up until this point. In the moments before Vegeta's tragic death, the Saiyan prince expressed confidence that Goku would become the legendary Super Saiyan and defeat Frieza. After Frieza murdered Krillin in cold blood, Goku's fury gave rise to a new level of power. As his hair changed to golden and his eyes to green, Dragon Ball's first Super Saiyan was born. Other Super Saiyans have followed, typically by similar methods. Anger has long been depicted as the trigger for the Super Saiyan form.
Early in the Universal Survival Saga, Dragon Ball Super takes another look at the inner workings of the Super Saiyan transformation in a scene that sees Universe 6's Cabba try to teach Caulifla how to go Super Saiyan in preparation for the Tournament of Power. When Cabba fails to anger Caulifla into making the transformation, Cabba tries a different approach by explaining that when he focuses all of his energy into his back, and as the power builds, he feels a strong, tingling sensation. From there, Cabba is able to access the form easily. With this knowledge, Caulifla is able to go Super Saiyan without getting angry.
Going Super Saiyan by channeling power into a person's back is a new and unexpected explanation for the Super Saiyan form, a concept that's always been centered around anger. The new explanation has been a point of contention for fans, as some have said that the change is a silly and unnecessary retcon. Others have argued that this explanation is only true for Universe 6, which would mean that it doesn't apply to most of the Saiyans on the show. However, it's since been confirmed that the change is canon for the main characters as well [via ComicBook].
It should be noted that the change answers a question that has puzzled fans for years. If the Super Saiyan form is triggered by anger, then how do characters like Goku, Gohan, and Vegeta access it on command? Apparently, each character had to be angry the first time, and that rage isn't required for any later uses of the form. Why it worked this way was never properly explained in Dragon Ball Z, but the new ideas expressed by Cabba in Dragon Ball Super provides the best explanation yet for Dragon Ball's most important transformation.