Understanding the problem isn't the same as having a failure-proof solution.
The moon's gravity is weak enough that we could land an entire two-person launch vehicle, and its launch platform, all at once, already in launch configuration, already fueled, and already flight-checked for launch. If anything had gone wrong, the Apollo astronauts were spring loaded to return home with a minimum of fuss.
On Mars, they'd have to assemble the launch vehicle, fuel it, flight check it, all in a hostile environment, and with their survival depending on getting it right. That's a lot of weight to put on the crew, first thing after touchdown.
I think it's solvable, but I'm still interested in the solution that ends up being used.
As for why this is my choice? Because I see it as the obvious and most pressing problem of a manned Mars mission: How to not make it a suicide mission.