Ecclesiastes 8:16-17

16When I applied my mind to know wisdom and to see the activities [of mankind] that take place upon the earth—how some men seem to sleep neither day nor night—

17and I saw all the work of God, I concluded that man cannot discover the work that is done under the sun. Even though man may labor in seeking, he will not discover; and [more than that], though a wise man thinks and claims he knows, he will not be able to find it out.