The fact how simple it is to re-implement a large part of Docker because all it fundamentally is a bit of glue code to the kernel is the biggest problem Docker-the-company faced and still faces.
Where Docker adds real value is not (just) Docker Hub but Docker for Windows and Mac. The integrations offer a vastly superior experience than messing around with VirtualBox and Vagrant by hand (been there, done that) to achieve running Docker on one's development machine.
replies(9):