What happens if one burns TWO-STROKE fuel in their vehicle?

pouring a gallon of 2 stroke fuel in the fuel tank of a car and then filling the tank with the correct fuel has never caused any problems for me and I have been doing that for many years. When I had an outboard it was not unusual to have several gallons of fuel left in the fall and adding it 1 gallon more or less at each fill up for weeks never caused a problem in the vehicles that I owned. Consider it upper cylinder lubricant that many people pay extra for.