Knowledge-based jobs were supposed to be safe career choices, the years of study it takes to become a lawyer, say, or an architect or accountant, in theory guaranteeing a lifetime of lucrative employment. That is no longer the case. Now even doctors face the looming threat of possible obsolescence. Expert radiologists are routinely outperformed by pattern-recognition software, diagnosticians by simple computer questionnaires. Algorithms and machines would replace 80% of doctors within a generation.