From Blessed John Henry Newman's Apologia pro vita sua, chapter 5:
FROM the time that I became a Catholic, of course I have no further history of my religious opinions to narrate. In saying this, I do not mean to say that my mind has been idle, or that I have given up thinking on theological subjects; but that I have had no variations to record, and have had no anxiety of heart whatever. I have been in perfect peace and contentment; I never have had one doubt. I was not conscious to myself, on my conversion, of any change, intellectual or moral, wrought in my mind. I was not conscious of firmer faith in the fundamental truths of Revelation, or of more self-command; I had not more fervour; but it was like coming into port after a rough sea; and my happiness on that score remains to this day without interruption.
Nor had I any trouble about receiving those additional articles, which are not found in the Anglican Creed. Some of them I believed already, but not any one of them was a trial to me. I made a profession of them upon my reception with the greatest ease, and I have the same ease in believing them now. I am far of course from denying that every article of the Christian Creed, whether as held by Catholics or by Protestants, is beset with intellectual difficulties; and it is simple fact, that, for myself, I cannot answer those difficulties. Many persons are very sensitive of the difficulties of Religion; I am as sensitive of them as any one; but I have never been able to see a connexion between apprehending those difficulties, however keenly, and multiplying them to any extent, and on the other hand doubting the doctrines to which they are attached. Ten thousand difficulties do not make one doubt, as I understand the subject; difficulty and doubt are incommensurate. There of course may be difficulties in the evidence; but I am speaking of difficulties intrinsic to the doctrines themselves, or to their relations with each other. A man may be annoyed that he cannot work out a mathematical problem, of which the answer is or is not given to him, without doubting that it admits of an answer, or that a certain particular answer is the true one. Of all points of faith, the being of a God is, to my own apprehension, encompassed with most difficulty, and yet borne in upon our minds with most power.