Why cars rust

About 12 years ago I saw a 1971 Duster for sale in Warren MI. Slant 6, auto, rubber floor, stripped down car. The owner was outside and I got the story on the car. He was an engineer and the car was a bet, he bet his friends that he could keep a car from rusting for 10 years. He told me that all he did was to keep it clean, and take it off the road in the fall and not drive it again until May. He drove it every day from May to October for 10 years, never parking indoors, even in the winter it would just sit uncovered in the driveway. Basically all he did was to keep salt from touching it. He won the bet, and kept the car for another 18 years. It still looked damn good in the late 90's when I saw it.