What's the logic behind Cell's zenkai?

[Natasha Romanoff]

Zenkais can't be inflicted by self damage as stated by Vegeta:


Do you think Toriyama retconed this or forgot about this line? Therefore this line would not have any more value from that point on?

 

[SSJ2]

Goku also did it while training on the way to Namek. Probably just an inconsistency.

 

[Kyo]

He probably just means that he’d subconsciously hold back if he tried to maim himself.

 

[Dagon]

His self-destruction could be a device rather than his own power. So it wouldn't count as self damage.

Vegeta also might be thinking of it as he won't be able to hurt himself because he'd have to make himself weaker but his attacks would also get weaker.