The purpose of software engineering is to control complexity, not to create it.
Incorrect documentation is often worse than no documentation.
Deleted code is debugged code.
When working on a problem, think only how to solve it. If the solution is not simple and has no inner beauty such as art, it is wrong.
Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction.