A "switching cost" is whatever you have to give up to switch between products or services - switching from Audible to a rival platform would cost you all your audiobooks, for example, thanks to Audible's DRM.
Facebook deliberately engineers its products to have high switching costs so that it can impose more pain on its users without losing them. So long as the pain of staying is less than the pain of leaving, Facebook calculates it can maintain its dominance.
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