Throw a pencil from a twenty story building and every kid knows that the probability of it landing on its head is close to zero. So, why is the SpaceX trying to do it?

As an engineer, I see this is one of those cases of failure by design. The rocket almost made it and that is amazing taking into account all the things wrong with the design they want to put in place. 

• You don’t land a stick on its head. It lands on its side, so the design should have taken that into account. Even if the CRS–6 could approach land vertically, they should have devised a way to lay it down. That would even allow for greater STABILITY AFTER LANDING (They almost did it by accident).
• Using the single rocket thruster to act as a fine attitude controller is dumb. You don’t use a hammer to perform eye surgery, but this landing project seems to be trying just that. This solution forces them to have one main engine with many variables to control power and direction. The uncontrollable aspects (degrees of freedom) are just too many.
• Another aspect that I don’t understand in this solution is FUEL. This solution needs a LOT of it. It is extra weight at launch because you need the fuel to bring the rocket to a standstill. All the weight could be used for cargo capacity to put more stuff in orbit. In the ’60s, they solved this problem by using something like PARACHUTES. Amazing isn’t it?

I know that Rocket Science isn’t easy. Trying to achieve this is a scientific challenge, but, as a scientist you sometimes come up with dumb hypothesis and TEST them, and TEST them, and TEST them until you either prove your hypothesis or you abandon it and make a new one. In this case, landing the rocket vertically has a big SHOWSTOPPER: It cost a LOT of MONEY for something a 5th grader knows is impossible to do.