Board Thread:General Discussion/@comment-5138166-20180117134112/@comment-28362353-20180121173342

That tingly back thing comes straight from a form of Japanese martial arts called Tanden, specifically the part involved in the concentration of your inner being/energy. So that tingling back is not bad writing at all. Goten and Trunks got SSJ with no explanation whatsoever, and Gotenks basically skipped SSJ2 and went straight to SSJ3 after seeing it only once. Yet no one complains about that.

Kale I can understand because she's so shy, but I personally felt like she got a lot better later on.