"People who introduce bad code do so because....they 'don't have time to do it right'....they lack experience maintaining code, or haven't learned the skills to

"People who introduce bad code do so because....they 'don't have time to do it right'....they lack experience maintaining code, or haven't learned the skills to write maintainable code....they 'have not heard of' things that 'should be' common knowledge" Those are all things that happen. But you're missing the most dangerous one of all: programmers who just don't understand how computers work. It's a surprisingly common problem, and it's a problem that algorithmic questions are especially good at identifying quickly. Hire these people at your peril, because while they are fine for simple tasks, they generally have no idea why their code is fast or slow, have no idea why their programs eat memory like a hog, and no idea how to begin to break down a difficult problem in a way that a computer might be able to handle efficiently. Give them a hard problem, and you might get something good....or you might get total garbage. It's programmer roulette. Programmers who don't understand computers are terrifyingly bad hires, because they can do the most damage before you catch them.