Be humble! Use public transportation!

It really is one of those "It depends on where you are." moments.

If you're in a car in the middle of northern Canada or Scandinavia - yes you CAN get out of your car and stretch your legs.
But do you really want to freeze your ass off? While in a train you can walk around without leaving it (which is a plus) and unless its fully broken down there will still be temperature control active so you'll stay warm while doing so.

In many cases if a train does break down and its clear that it won't be going anywhere they'll even let passengers off in my experience.
Though again, it depends on where you are whether that is practical or not.
Similarly, for both car and other forms of transportation (boats also fail, as do planes but fewer people go around casually with those).
Depending on where you are you can have alternate transportation or assistance come to you within a matter of hours or not at all.

I know that overhere (Netherlands) neither are too bad as they generally have alternatives available on shorter notice.
There are a number of services targeted specifically to assist people who end up having their vehicle break down on the road.
And these services often also have some form of coverage when you're abroad. ^^
So it ends up being six of one and half a dozen of the other - while vehicles breaking down obviously throws a wrench in your plans, its hardly the end of the world.

And if you had taken another vehicle there are a number of thing that could've gone equally wrong.