“I am nevertheless greatly saddened, for such questions mean that the inquirers have not really known me, my commitment or my calling. Indeed, their questions suggest that they do not know the world in which they live.”

cannot be answered, because we have no experience or authentic information from which to answer it; and that any answer only throws the difficulty a step further back, since the question immediately presents itself, “Who made God?”
Source: Autobiography (1873), Ch. 2: Moral Influences in Early Youth. My Father's Character and Opinions.

Psycho-Pictography

Source: The Wizard of Zao (1978), Chapter 5 (p. 65)

Confessions of a Philosopher (1997)
Context: Speaking for myself, I am not one of those people who are able to deal with the problem by ignoring the questions: it may be a matter of temperament, but for me the apparent unanswerability of the questions sharpens the persistence with which they nag at my mind. Scarcely a day has gone by since my childhood in which I have not thought of them. In fact, the truth is that I have lived my life in thrall to them. They seem to me obviously the most important and interesting questions there are, and in my heart of hearts I do not really understand why not everybody sees them as such. And yet at the end of it all I have no solutions. I am as baffled now by the larger metaphysical questions of my existence as I was when I was a child — indeed more so, because my understanding of the depths and difficulties of the questions themselves is now so much greater.

"Prayer Before Birth", line 11

Letter to his brother Rev. William N. Cleveland (7 November 1882); published in The Writings and Speeches of Grover Cleveland (1892), p. 534.
Context: I feel as if it were time for me to write to someone who will believe what I write.
I have been for some time in the atmosphere of certain success, so that I have been sure that I should assume the duties of the high office for which I have been named. I have tried hard, in the light of this fact, to appreciate properly the responsibilities that will rest upon me, and they are much, too much underestimated. But the thought that has troubled me is, can I well perform my duties, and in such a manner as to do some good to the people of the State? I know there is room for it, and I know that I am honest and sincere in my desire to do well; but the question is whether I know enough to accomplish what I desire.
The social life which seems to await me has also been a subject of much anxious thought. I have a notion that I can regulate that very much as I desire; and, if I can, I shall spend very little time in the purely ornamental part of the office. In point of fact, I will tell you, first of all others, the policy I intend to adopt, and that is, to make the matter a business engagement between the people of the State and myself, in which the obligation on my side is to perform the duties assigned me with an eye single to the interest of my employers. I shall have no idea of re-election, or any higher political preferment in my head, but be very thankful and happy I can serve one term as the people's Governor.

When he quit BBC due to differences with John Birt, the Director General of BBC.
Source: Peter Victor, " Tully quits BBC http://www.independent.co.uk/news/tully-quits-bbc-1412865.html," The Independent, 10 July 1994

Inquired of, that is, by men rather than by scholars. There is a man in each scholar, a man who inquires and stands in need of answers. I am anxious to answer the scholar qua man but not the representative of a certain discipline, that insatiable, ever inquisitive phantom which like a vampire drains whom it possesses of his humanity.
in Franz Rosenzweig: His Life and Thought (1961/1998), p. 97