Answer:
It's simple, right?
Explanation:
In episode 95 (or the twenty first episode of the Frieza saga) it was shown, at the near end of the episode, Freeza used Death beam to finish off Goku, but Piccolo shoved Goku away and sacrificed himself, putting him at near death. Freeza then used Telekinesis and took Krillin up to the air, then blew him up (also called Dirty Fireworks). This caused Goku to rage, with the fact Freeza killed Krillin without mercy, with the rage swelling up, so did is S-cells, causing Goku to turn Super Saiyan (Sūpā Saiya-jin in Japanese). In the World Tournament saga, in episode 214, Goku turned Super Saiyan 2 (Sūpā Saiya-jin Tsū in Japanese) Goku trained in the Other World to achieve Super Saiyan 2 to defeat Majin Vegeta. In episode 245 of the Majin Boo saga (also spelled Buu in English dub) when Goku was showing Majin Boo and Babidi (Majin wizard) his transformations, Goku then pushed his own limits, Goku transforming to Super Saiyan 3 made the Earth shake, causing everything to shake or break. With the possibility of killing some innocents due to Earth shaking violently. With his power swelling, this form can also cause a power strain on the user, depending on the Saiyan's Power level. With Vegeta, knowing the power strain of a Super Saiyan 3, he skips the transformation and rather turn Super Saiyan 2 or Super Saiyan Blue (SSGSS, or SSJGSSJ). This means Super Saiyan can be achieved by either emotional, near death, or by pushing their own limits.
