KISS Principle by Kelly Johnson
Keep It Simple, Stupid!
You Ain't Gonna Need It
New Jersey Style by Richard P. Gabriel
Worse Is Better
There is a point where less functionality ("worse") is a preferable option ("better") in terms of practicality and usability.
DRY Principle by Andy Hunt and Dave Thomas
Don't Repeat Yourself
If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.
I Know It When I See It by Potter Stewart
Murphy's Law by Edward Aloysius Murphy
Anything That Can Go Wrong, Will Go Wrong
Sturgeon's Law by Theodore Sturgeon
Nothing Is Always Absolutely So
Parkinson's Law by Cyril Northcote Parkinson
Work Expands So As To Fill The Time Available For Its Completion.
The amount of time which one has to perform a task is the amount of time it will take to complete the task.
1% of people create content, 9% edit or modify that content, and 90% view the content without contributing.
Pareto Principle by Vilfredo Pareto
80% of your complaints come from 20% of your customers.
80% of the effects come from 20% of the causes.
And at the end the great words of Joshua Bloch ("Effective Java programming"):
Learning the art of programming, like most other disciplines, consists of first learning the rules and then learning when to break them.