I think the rest of the paragraph you’re reacting from goes into why he believes this, after a long career of writing video games: Programmers will test for al

I think the rest of the paragraph you’re reacting from goes into why he believes this, after a long career of writing video games: Programmers will test for all the conditions they can imagine, but a good tester will imagine many many more and players will try things programmers never even considered. Knowledge of their code is the achilles heel of programmers. I've had code I was 100% sure was rock solid, only to have one of our testers reduce me to tears. A good tester excels at poking your code in places you never considered. I'm not talking about your unit tested sort routine, I'm talking about complex puzzle logic and odd UI uses. It's the stuff unit tests will never catch, but a good tester will. Testers are the unsung heroes of your team, treat them very well.