There are many quotes from famous computer scientists that have become the wisdom that guides our profession. For example:

"Premature optimization is the root of all evil in programming."

• Donald Knuth (citing Hoare's Dictum)

"Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it?"

• Brian Kernighan

And so on. My question is, what are your favorite words of wisdom about programming from someone who is not famous? Was it a friend, a coworker, or a teacher, or a family member?

For example, a technical writer friend of mine said:

"You can't get the right answers unless you ask the right questions."

Thanks for all the contributions! The answer I selected was (a) specifically coding-related, and (b) stated by someone who is not technically famous (though he has a popular blog and a podcast and runs StackOverflow). I.e. he's no Bill Gates or Yogi Berra.