Any fool can write code that a computer can understand. Good programmers write code that humans can understand. - Martin Fowler

Often you'll see the same three or four data items together in lots of places: fields in a couple of classes, parameters in many method signatures. Bunches of data that hang around together really ought to be made into their own objects.

Often designers do complicated things that improve the capacity on a particular hardware platform when it might actually be cheaper to buy more hardware.

The key is to test the areas that you are most worried about going wrong. That way you get the most benefit for your testing effort. It is better to write and run incomplete tests than not to run complete tests