You say that with such certainty. I may be thick, but I haven’t seen enough to be convinced whether or not they know what they are doing and what problems are solved or unsolved.
How do you know?
How do you know?
But, if you want to know exactly why going to Mars is so difficult, and why so many projects have failed, start here: http://en.wikipedia.org/wiki/Exploration_of_Mars#Probing_dif...
Or simply do a quick search on the internet for 'Mars difficulties' or 'Mars curse'.