Sometimes it’s enlightening to pretend you’re explaining a phenomenon to an alien.
Let’s say you have an alien by your side who doesn’t know what a car or a bike is. You would say:
These are two means of transportation for humans. One of them is powered by fuel, the other one is powered by human energy. Get it? (You have to be pedagogical with these aliens.) In the first case, no human energy at all is needed. It doesn’t matter if the road goes up or down, you basically just push a button and lean back. Whereas in the second case, only your own energy is what moves you forward. So everything that slows you down – upslopes, curves, road bumps – will demand more energy of you.
The alien now has a clear image of the two means of human transportation. Then you ask it:
Let’s say you want to separate these two means of transportation. You want to build two different types of roads for them. Now, let’s say you build one road that is straight and smooth, and another road that is curvy and full of road bumps from tree roots. Which one would you give to the fuel powered type of transportation, and which would you give to the human powered one?
That’s too easy! the alien would reply. Even I get that it would be better to give the straight and smooth road to the human powered method, because it would demand less energy from you, and the only energy you got is your own. Whereas the fuel powered method can make do with a less smooth road, since you just push a button to move forward anyway.
Then you explain to the alien that it is the opposite way around: The road for human powered things goes in crooks and circles around the straight road for fuel powered things, often crossing it every few hundred meters, causing extreme loss of human energy. In addition, these winding “roads” are so cheaply built that they quickly deteriorate, with tree roots penetrating the surface in a way that doesn’t happen in the more expensive road made for fuel powered things.
The alien is of course shocked! Then it realises:
Oh, I must be missing something. Maybe the fuel powered method is very sensitive to bumps? Maybe every tree root in the road makes the fuel powered thing really uncomfortable to drive? And the people on the human powered things don’t mind these roots?
And you reply that no, it’s actually the opposite way around in this case too; the fuel powered things – and by now you can reveal to the alien that they are called cars – actually weigh a thousand kilos and have thick tires and heavy suspension, whereas the human powered things – ok, they are called bikes – are extremely sensitive to tree roots and other hindrances in the street.
But then I don’t understand at all, the alien says. On my planet we’re fostered with a very logical way of thinking, but this isn’t logical at all to me. If what you’re saying is true, then why are the roads for what you call “bikes” often made of uneven stones, while the road for “cars” next to it is smoothly paved? And why is the “bike road” constantly interrupted by cobblestones, when the “car road” is not? The alien shows you a photo:
Why? The logical alien doesn’t get it. And frankly, neither do I.