Any fool can write code that a computer can understand. Good programmers write code that humans can understand.
Martin Fowler's Wikiquote page is a diamond mine of aphorisms.
Often designers do complicated things that improve the capacity on a particular hardware platform when it might actually be cheaper to buy more hardware.
Analysis Patterns: Reusable Object Models, 1997
Modeling Principle: Models are not right or wrong; they are more or less useful.
Refactoring: Improving the Design of Existing Code, 1999
When you find you have to add a feature to a program, and the program's code is not structured in a convenient way to add the feature, first refactor the program to make it easy to add the feature, then add the feature.
When you feel the need to write a comment, first try to refactor the code so that any comment becomes superfluous.
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.
UML Distilled: A Brief Guide to the Standard Object Modeling, 2004
Comprehensiveness is the enemy of comprehensibility.
Martin Fowler deserves a knighthood.