according to his own admission, he's a prodigy so he never had to work for anything in his life, he was always hella strong (similar to how some people are "born genius'" they dont have to cram or study for finals like the rest of us, learning is super-simple for them). after he was revived with the Dragon Balls he concludes that if he trains for several months then he will be able to defeat the Saiyans. as a result he has attained a massive golden power-up. thats it, really