So, I've seen A LOT of people state that they dropped the show the moment Kale and Caulifla achieved Super Saiyan through the "tingly back" method. Turns out, in terms of Buddhism (one of the largest religions in Japan), it's common knowledge for the back to be the point of emotion. Geekdom101 (the most factual and true Dragon Ball YouTuber) and Kendamu (martial arts expert) explain it in the following video: 

https://youtu.be/zFqAvcuuCeA

In short, in Buddhism, when meditating, there are 3 points at which your energy is channeled to Shin (inner spirit or God; between your eyes), Ge (energy in your naval area), and back up to Ki (life energy in the upper back). 

What's the energy source of Dragon Ball? Ki. So, in terms of Buddhism and Japanese common knowledge, the tingly back method makes sense. In fact, it explains why Saiyans don't need to become angry every time to go Super Saiyan. It's because, through trial and error, Goku and Vegeta learned that the best way to go Super Saiyan effortlessly is through channeling their energy to that point and letting it explode. Then, upon learning this, their findings were taught to the next generation of Goten and Trunk (possibly even Pan and Bulla in the future). 

Anyways, I hope you learned something and I hope you have a great day! ^^ Also spread this information to all of your Dragon Ball friends! 

Tags for those who I think might need to see this:

HayleyDBZ
DaddyGoku