But the underlying fallacy — the failure to notice that things must add up — is, in my experience, the single greatest source of economic error. Politicians routinely promise to make medical care or housing or college educations more widely available by controlling their prices; economists routinely scratch their heads and ask where the extra doctors or houses or classrooms are going to come from. You can no more speed up the line for medical care by lowering prices than you can speed up the deli line by handing out tickets.