I believe this demonstrates that man's own thoughts are inadequate for understanding without the constant feedback which comes from observation. It is our nature to ask and to seek to know how things work. We count our knowledge correct when we can repeatedly predict an outcome with cause under control. Our desire to know meets our destiny to know when what is real is revealed to us - and the correction that ensues steers us ever towards our goal.
Take the understanding of light itself as an example. Light travels very fast - something like 671,000,000 miles per hour. Past a small threshold, big numbers are meaningless to humans, because we cannot easily appreciate the difference between 100,000 miles per hour or 1,000,000 miles per hour and 671,000,000 miles per hour in everyday terms. All those speeds make the time for a trip to the grocery store something smaller than we can perceive (unless you live in Houston).
Knowing what we know now, it's easy to chuckle at Galileo's attempt to measure the speed of light using a mile of separation, an assistant, and two lanterns. But the speed of light can be measured, and it comes out to some number that's quite easy to express on paper. It is limited. You just need the correct scale to measure it upon. Later a Danish astronomer named Ole Roemer found a more appropriate scale upon which to gauge the speed of light - the massive scale of our solar system. Using measurements of the observed timing of the movement of Jupiter's moons he was able to get the first good approximation for the speed of light.

Take a look at the this submerged object to the right. Now, I want to test what you believe about this object. You may have read about it, you may know its history, someone may have told you about it, or you may be seeing it for the first time. What I would like to know is, what do you believe about it's origins? This thought experiment would be even better if you hadn't known anything this object previously and further valid if you had little knowledge about how fluid flow may affect a metallic structure and produce patterns of any kind (also if you couldn't google it either.)
So what do you believe? Did the sea's currents shape this piece of bronze, or did bio-erosion from the coral reef's attached to it? Did a human once shape it and then dump it into the sea? Some submerged statues we know are very old. How old do you think this one is? How would you tell?
If I told you that the waves did so happen to shape this object and there was nothing more to it, would you believe that? No thinking person could settle for that. The drive to resolve coincidence and look for a cause would not leave my shallow explanation alone.
This common human longing for knowing cause and effect, for being able to reason out why things happen, this common suspicion that purpose has origins, that images have objects from which they are derived, this longing for unity, is itself a unifying factor through which all humans can relate to one another.
Some things are too far or too small for us to see sometimes. Without the recorded knowledge that we have modern man would be just as pitiful with some of his assumptions about how the world really operates. But there is truth. Sometimes we don't have the vision to see that truth, and even other times even if we can see it we reject it. We reject it because we already gave up on that question long ago - and we have settled for our substitute answer.
Have you ever studied mythology? It's confusing. Our stories, when untethered from reality, go in every which direction. But I will often appeal to this - that there is only one truth. There are many varieties of things that may be said about that one truth - a variety that is celebrated by the diverse landscape of people we find in our world. However, variety must be tethered to what's real to be veracity. Adding to the belief that there is a single truth, it is true that we have a desire to obtain it. Though at times we settle for something less; our own actions betray an underlying belief that the rational mind demands a logical cause and effect relationship. Finally, we embrace this belief in cause and effect when we look for the answers to who we are and what we are doing here. Though at times settling for an inferior explanations, our decisions and professions betray that we know more about the nature of our origins than we let on. Not that we see it clearly, we do not. It must be illuminated for us. But deceived or not, we all bear this burdening question that we must answer in one way or another: why?