99.9% ISN'T GOOD ENOUGH
Standing at the urinal, taking care of business, I noticed that the soap available for the post-urination ablutions confidently proclaimed it would kill 99.9% of all germs. That many, huh?

But it isn't those 99.9% that you have to worry about; it's the other 0.1% that live on. Think about it - you've managed to kill off the pathetically weak germs, living only the strong behind. And what do those strong germs then do? That's right: bonk themselves stupid to create new germs, some of which are now able to resist the 99.9% soap.

Over time, only those germs that are strong enough to resist the disinfectant and breed become the dominant germ species. Our 99.9% effectiveness crawls down to 90, then 80, then 70, until you might as well just wash your hands in your own urine.

We, the human race, are then faced with the task of creating new 99.9% solutions, which in turn produces a fresh batch of 0.1 germs that are even stronger. By acting as an agent of natural selection, we sow the seeds of our own pathogenic destruction. At some point, we'll face a germ that kills us all off. This is how the world ends; not with a bang but with a sneeze.

Of course, we may be lucky. The killer germ might only kill 99.9% of humanity, leaving a resistant 0.1% to begin the whole process over again.