Engagement alone is not success but sustainable and improving engagement (I.e. strong and improving cohort retention) is a measure of success because it creates a high barrier of exit for you as a user to stop using the app. 74 mins daily is not easy to create and sustain especially when you don’t have a social graph (On Facebook you are spending time talking to friends, reading updates from friends and content) but on Toutiao - you are only consuming content.