Mistakes are human...
...and humans make mistakes making robots. Flying them too. Seriously, I believe one 500 day human mission to Mars would learn more about the Red Planet than probably 500 robotic missions. Humans won't take 3 weeks to point a microscope at Martian soil. And don't forget the humans who go will bring robots with them too. And when the robots inevitably break down the possibility will exist to repair them.