stepbackj34spud
Top 75 All-Time
Its basic logic. If Goku can't use it in a human body without destroying his stamina, what makes you think he ever would've figured out how to do it in his living body in the first place? It's not like USSJ or Frieza's 100% power where he's just pumping up his Ki more, it's a whole transformation that was only ever achieved by a dead guy with no Ki and a magical fusion. The only way the form is even conceivable is if you have no Ki or stamina to worry about. That's why Vegeta never bothered with it. He and Trunks had to learn how to reach that power naturally as Super Saiyan 2
You call it basic logic. I call it head cannon.