Question about Tenacity and definition

I appreciate the response! I do understand stun is predetermined by which toon does the stunning, I guess I should have finished my thought that I was more talking about "Specia Events" where the team you're going up against is a team the developers put together!and those toons don't seem to follow the same rules...Last thing, the stun length is predetermined or supposed to be but how is that there are times when I stun another toon and it lasts for only a second or if my Aayla gets stunned there are times it goes away right away?