The law of existence.
Nevertheless, nobody knows if he/she will survive or not. And everything is trying to protect itself. Those perfect ones don't think of it - the Universe is for them, they only struggle with each other for things that mean less than nothing in the other part of the world. This part's destination is survival. Or, at last, existing as long as possible. Here is where different ways of defence come from. The most effective of them is attack.
If I see danger, I try to give that person a strong unexpected bite at once. While he/she is trying to get better after the painful shock, I will have some time to run away. Yes, maybe he/she will catch and defeat me in a short time. But at least I'd die with a thought I've also hurt him or her...