It is possible to build a self sufficient colony on Mars and it is also Elon's stated intention. It is not an easy task and we will have a permanent colony before we have a self sufficient one, if we have a colony at all. 66 years passed between the Wright brothers first powered flight (which lasted only 3 seconds) and landing a man on the moon. That is a huge gulf in technology. Perhaps we will have a self sufficient Mars colony in another 66 years.