Board Thread:Questions and Answers/@comment-30088034-20170219194117/@comment-26887879-20170222184930

Flowey says that here (one of neutral endings): https://www.youtube.com/watch?v=V5tX0GyG3_I

There is belief that previous human's (before Frisk) couldn't reset or that Frisk and Chara could only reset because they have red (assumably most powerful) soul. However that wasn't confirmed yet...