> What, exactly, is that guy doing for those five years?

Waiting to be rescued. We're not talking about sending one guy to mars for funsies, we're talking about one person left after an emergency. In the book he gets off mars by going to the launcher staged for the next mission, which again is a case of prepositioning extra hardware before sending someone to the planet.

If you assume a team of 5 people with an intended stay of 6 months, 5 years of supplies is a factor of safety of 2. If you send enough supplies to keep the whole team alive till the next launch window, that would keep a single person alive for about 2 decades (ignoring potential storage lifetimes).

> In the book he gets off mars by going to the launcher staged for the next mission, which again is a case of prepositioning extra hardware before sending someone to the planet.

There's a "world" of difference between the Eagle returning to Apollo 11 in low lunar orbit, and prepositioning a interplanetary vehicle capable of Mars-Earth (after getting from Earth to Mars), landing it (and without live feedback/guidance, because of roundtrip radio time, not to mention, this isn't some Rover, it's a really large rocket) well in advance of the manned mission (8 month flight time, IIRC, which means realistically it's going to be hanging out on Mars for a minimum of 6 years, even if you launch the manned mission within a couple of months of its arrival, which seems ... risky) and hoping that one solo astronaut is going to be capable of fixing any issues that arose during landing or during its ~year, untouched, and five years of his habitation.

Martian dust storms are a thing. "Smaller", continent-sized ones lasting weeks at a time, hit a few times a years. And then you have the planet-covering ones.

> Individual dust particles on Mars are very small and slightly electrostatic, so they stick to the surfaces they contact like Styrofoam packing peanuts.

So many issues. We're not solving these by 2035.

We are still at the point where unmanned, tiny craft with none of these challenges routinely fail. We're making progress, but we're not making that much progress, not that quickly.