" To think that just when one's happiness is full to overflowing, and one is thoroughly in love with life, there should come upon one a taint of sorrow!" she murmured.

Yes; such is the payment exacted for the Promethean fire. You must not only endure, you must even love and respect, the sorrow and the doubts and the self-questionings of which you have spoken: for they constitute the excess, the luxury, of life, and show themselves most when happiness is at its zenith, and has alloyed with it no gross desires.
Such troubles are powerless to spring to birth amid life which is ordinary and everyday; they cannot touch the individual who is forced to endure hardship and want. That is why the bulk of the crowd goes on its way without ever experiencing the cloud of doubt, the pain of self-questioning. To him or to her, however, who voluntarily goes to meet those difficulties they become welcome guests, not a scourge.

But one can never get even with them. To almost every one they bring sorrow and indifference.

Yes; but that does not last. Later they serve to shed light upon life, for they lead one to the edge of the abyss whence there is no return--then gently force one to turn once more and look upon life.
Thus they seem to challenge one's tried faculties in order that the latter may be prevented from sinking wholly into inertia. "

― Ivan Goncharov , Oblomov