## That Daily Shower Can Be a Killer

That is the title of a recent article in the NYT. The author talks about his experience with New Guinea natives who refused to camp under dead trees. The reasoning being that there is a 1 in 1000 chance of one falling over, I sleep under trees every night, if a tree lands on me it will kill me, the mathematical likelihood is 100%.

The author uses another example of taking a shower (hence the name) and it’s likelihood for older individuals.

I started to think about computer stuff. If you think about some of the systems you have developed or used you may have similar concerns:

- that disk drive that has a 0.01% failure rate
- the expected occurrence of a divide by zero
- neatly computed mtbf for that system delivered

All of these fall into the same case: with large numbers any percentage greater than zero will cause a failure.

Currently working on student course selection software. It has been painful dealing with the number of special cases that have to be hacked into otherwise pretty good looking code. Why on earth do we care about these odd cases?

Using the above logic, “any expected failure will occur” in this case with a large number of students over a period of time, it becomes clearer – the system will fail. It is just a matter of time.