As Washington discovered with semiconductors, export controls that aim to maintain a technological lead are double-edged. They may slow a rival’s catch-up, but they also incentivize the rival’s innovation and harm domestic interests. And they are hard to enforce. China is rapidly expanding its export controls to include not just rare earths but many other technologies where it has a lead. But the more controls it imposes, the more it risks choking off revenues and paths to innovation for its leading tech companies.