The Martian is a survival story because almost every problem becomes a measurement.
Mark Watney counts food, energy, water, and time instead of waiting for luck.
His potato plan uses Martian soil and his own waste because the bottleneck is calories: rescue only matters if he can stay alive long enough.
That turns survival into resource management. Each improvisation buys time while creating a new constraint somewhere else.
The drama is not just whether he is brave. It is whether the math leaves him enough days to be rescued.