"Besides the inherent potential for paradox?" Because that had been a pretty big one--and they'd still taken the risk. Trunks sighed, meeting that look easily. "Better we risk it and try and prevent what happened in my time, from happening elsewhere." Putting the soda aside and entirely serious. "In the year 764, my world's greatest Hero finally kills one of its greatest threats. Then 6 months later he dies from a virus that attacks his heart. Which means, 3 years later in 767, on May 12th, there's no one to stop two advanced Androids from starting their reign of terror. All of the other warriors who stood any kind of chance were killed. I was just a baby. The man who would eventually become my master, was a pre-teen."