Expect the Unexpected

The magic of the unusual things

They say that some people see the glass half full, some see it half empty. But most programmers
don’t see the glass at all; they write code that simply does not consider unusual situations. They are
neither optimists nor pessimists. They are not even realists. They’re ignore-ists.
When writing your code don’t consider only the thread of execution you expect to happen. At every
step consider all of the unusual things that might occur, no matter how unlikely you think they’ll

By Pete Goodliffe

From 97 Things Every Programmer Should Know