Because no matter how you disinfect it, it may not be completely eliminated. You can eliminate it, but the rest is less than 0.00438+0%. So it is often replaced by five 9s. Then we all know that many times what we do is accidental and universal, and we often talk about accidental things in experiments in mathematics or other disciplines. Then when we are also doing these disinfection and sterilization, there may be accidental things, but they will not be so absolute, just like China's modest tradition. Although we said that the operation should be disinfected, there are still many cases, although we have done a good job of disinfection and prevention. However, patients will still be infected because of a large area of wounds. First of all, they may not be able to do 100% in disinfection and sterilization. Why? 100% let's not talk about it. In fact, this is very similar to what many people say when they promise one thing, not that I 100% can do it, but that I will try my best to fight for it. This is the same meaning. Many times, we can't completely say that it will be realized, because there will always be such accidents.