Why was Mark Watney stranded on Mars in The Martian?
In the first chapter of Andy Weir's The Martian, astronaut Mark Watney—the book's protagonist—becomes stranded on Mars due to a storm and a technological failure.
Mark was a member of Ares 3, NASA's third manned mission to the red planet. Shortly after landing on Mars, Watney and his crewmates encounter a major storm system that their equipment is not built to endure. Consequently, NASA tells the Ares 3 crew to abort the mission, board the Mars Ascent Vehicle (MAV), and rendezvous with the Hermes shuttle, which was in Mars' orbit.
The crew races to get off Mars, but by this point the storm is raging. The crew can barely see in front of them, so they rely on the technology in their suits to help them reach the MAV and locate any crewmembers who get lost.
Unfortunately, the storm knocks a communication dish off the crew's Mars base camp and slings it into Watney. He goes flying across the Martian landscape and loses consciousness. Moreover, the dish breaks his biometric computer, which makes the rest of the crew believe he is dead. Thus, they board the MAV and leave Mars—and Mark Watney—behind.