To ask Why is to seek into the cause of an effect or the reality behind an appearance. This is what man has been doing from the moment he was hatched from the cosmic egg.
In other words, to ask why something happens is to ask what causes it. The cause is presumed to be greater than the effect. Everyday experience shows us that something is "lost" or dissipated between a physical cause and its effect, AKA entropy.
The Principle of Sufficient Reason puts forth the controversial -- because inconvenient -- principle that "nothing is without reason" and that "everything must have a reason or a cause." We consider it soph-evident that:
"For every entity X, if X exists, then there is a sufficient explanation for why X exists. For every event E, if E occurs, then there is a sufficient explanation for why E occurs." And "For every proposition P, if P is true, then there is a sufficient explanation for why P is true."
Remind us, what is wisdom? Wisdom has to do with ultimate causes, or the highest cause. Thus, the sufficient cause of wisdom must be God. Conversely, the sufficient cause of lesser forms of knowledge is found in, say, material interactions, or the laws of physics.
You might say that everyday science is "caused" by the world (or causes within the world), whereas the higher science of theology is caused by God.
However, science as such must also be caused by God, unless you simply stop asking why, or else tautologically confine your whys to a single level.
You parents out there will have noticed that even -- especially? -- a child won't fall for that one. They cannot be satisfied with some explanation that simply displaces the cause a little further back. You could explain the Big Bang in every detail, but the most elegant explanation withers in the light of just one more innocent Why?
The whys can only stop at God. Since God is the uncaused cause, he is by definition the source and end of the Whys.
We've been discussing this in the context of one of the greatest Whysmen of all time, Thomas Aquinas (or St. Thomas, his AquWHYness).
McGinn notes that the Summa contains "over a million and a half words divided into three large parts containing 512 topics ( questiones) and no fewer than 2,668 articles..." It is sort of an inverse fractal: questions within questions within the Question.
"Thomas says that all wisdom comes down from God," like water from the mountaintop. "In communicating true teaching to make the earth (i.e., their hearers) fruitful, they [teachers of divine doctrine] do not depend on themselves." Rather, "God communicates wisdom by his own power, so he is said to water the mountains by himself."
Thus, the best we can hope to be is a curious waterboy. And in order to be an effective water carrier, we need an empty bucket, or a bucketfull of Why. And be sure to check for holes. You want a big one at the top.