"The time it takes the Phoenix Mars Lander to streak through the atmosphere and set down on the dusty surface has been dubbed "the seven minutes of terror" for good reason. More than half of the world's attempts to land on Mars have ended in failures."
To be more specific, humans are currently batting .384 (5/13) for Mars landing attempts. Considering the money and effort to get there, you would think someone would just think to put the equipment in a big ball of iron and hope to God it lands, but obviously that hasn't happened yet.
And an interesting quote from Al Jazeera:
"It's kind of like going to Vegas. If you have high odds, you play a number of times, eventually one of them is going to bite you," Barry Goldstein, project manager of NASA's Jet Propulsion Laboratory, said.