True, but Amazon could easily be profitable. It is a matter of choice in their case and has been that way since the beginning if my memory serves. Jeff Bezos chooses to run the company more like a non-profit than a C-corp. On the other hand, Groupon never had a sustainable business model.

Twitter seems like they could have a sustainable business model which is good, but I haven't seen much proof so far. When Facebook was not profitable for so many years, it was fairly obvious to me they had a path to profitability or sustainability (if they chose to act like Amazon). It is not obvious to me how Twitter will do this.