The problem is not completely reversible (in practice) because when parking, you have a goal that does not allow for much variation (as parallel as possible, not too close to the other cars, not too far from the curb, ...) and some intermediate states force you to get out and start again.When leaving a space, there's a lot of room on choosing when to leave the spot (as soon as possible, just clearing the other car, with more speed because of incoming cars, etc.) and you can switch from one possible solution to another at a relatively low cost.The practical (not computer assisted) problem is that we behave much more tentatively with parcial/imperfect information.