The fact that humans can do so many things that robots cannot yet do. Look at it the other way: what is the most robust and fault tolerant adaptive machine with the best motor skills, the best perception system, and quick decision making system that we have available? There are some tasks that robots are better at, but as a general purpose machine humans are still the best. A robot tumbles over or gets stuck behind a stone, and you've just lost your multi billion dollar project.