Rare but often important. We all work with computers all the time, and so we have a tendency to try to represent the universe in the simplest abstractions that

Rare but often important. We all work with computers all the time, and so we have a tendency to try to represent the universe in the simplest abstractions that capture the necessary detail for the project we are currently contemplating. When those abstractions fail to capture a necessary detail, it can be due to: - a bad abstraction in the first place - a new use for the representation that we hadn't thought about - insufficient understanding of what we are trying to represent I have seen all three of these situations repeatedly. They are all quite common.