Im not questioning your intellect, but each database has its own use case for usage. You might be expecting wrong things from Mongo or cassandra. Using gazillion databases for wrong use cases doesnt mean nothing. From your child comment, you cooked up an in house solution, it may be best suited for you. But for others it would be horrible too. If Cassandra is suited for Facebook, I think the problem is with you making a choice to use it for something its not suited for rather than the database itself.