And if you look at the gradual addition of features to Instagram that Krieger describes you will find that theyallanswer these type of questions: will this prompt the user to take or share more pictures, will it make the process easier or faster, will it be more fun and fulfilling for the user and their friends?
It means they are all hellishly clever and knowledgable, but whenever you present a number of them with the same business problem theyall come out with an identical answer because they have all learnt it from the same book.