After code review, I understood why people say bad programmers destroy wealth. Their productivity is less than 0, which means they are creating bugs and drag the team to fix it. I consistently saw really bad and buggy code here and there, by one programmer who is not at our company. But the code there is guaranteed to be bad, and buggy. Interestingly, bad programmers are very productive if you measure by lines of code they created. So identify them! Early!