The success of platform businesses like Alibaba, Airbnb, and Uber is so remarkable that discussion about them often misses just how hard they are to build. For every successful platform, there are many more that struggle or simply don’t make it. Apple and Google, two of the world’s most valuable companies, have had their share of platform failures as we’ll show. Studying these successes and failures, we’ve identified half a dozen key reasons platforms fail, all of which boil down to managers’ misunderstanding of how platforms operate and compete.