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

Martin Fowler

Entities must not be multiplied beyond necessity.
Occam's razor

Most good programmers need to think twice to understand expressions with side effects. Let them use their brain cells to understand the larger questions of how your code works rather than the syntactic details of a specific expression.

Steve McConnell, Code Complete, Second Edition

It's almost impossible to identify performance bottlenecks before a program is working completely. Programmers are very bad at guessing which four percent of the code accounts for 50 percent of the execution time, and so programmers who optimize as they go will, on average, spend 96 percent of their time optimizing code that doesn't need to be optimized. That leaves little time to optimize the four percent that really counts.

Steve McConnell, Code Complete, Second Edition

Complicated code is a sign that you don't understand your program well enough to make it simple.
Steve McConnell, Code Complete, Second Edition