Why Goku Is Stronger Than Vegeta
There have been times in the series where they explained why Goku is stronger than Frieza. But, a reason I always thought is because Vegeta doesn't rest enough when in real life our bodies need rest to recuperate and get stronger. Not resting could put too much stress on your body. We see this with Vegeta when he was preparing for the Androids, and Cell.
Goku on the other hand is stronger, but rests a little too much. We clearly see this on his fight before Cell as after he exits the hyperbolic time chamber, they have like 5 episodes where we see Goku do nothing more than relaxing in his Super Saiyan Form.
This is a weakness explained by Whiss in the movie. Vegetal doesn't rest enough, while Goku rests too much.