[lotharbot]

> "If you keep rolling a thousand dice, eventually they will all come up sixes"

A thousand sixes in a single simultaneous roll shouldn't happen in the entire lifetime of the universe. If your system is that safe, you're in pretty good shape. But rolling a thousand dice where you get to set aside each six you get, you should expect to get to all sixes in 30 or 40 rolls.

Whenever you're engineering a system for safety, the key is figuring out how much needs to go wrong for the system to fail, and how many opportunities you'll have for those things to go wrong. Diseases being carried from continent to continent is a fairly normal occurrence; contamination will happen fairly regularly, and the biggest protection against it becoming widespread is herd immunity.

[setrofim_]

Yes, true. My thousand dice comment was intended in vein of "if you put a thousand monkeys with typewriters in a room...". I did not mean to imply that the probability of rolling a thousand sixes is similar to the probability of contamination.