In Mere Christianity, C. S. Lewis writes:
Before we can be cured we must want to be cured. Those who really wish for help will get it; but for many modern people even the wish is difficult. It is easy to think that we want something when we do not really want it. A famous Christian long ago told us that when he was a young man he prayed constantly for chastity; but years later he realised that while his lips had been saying, “Oh Lord, make me chaste,” his heart had been secretly adding, “But please don’t do it just yet.” This may happen in prayers for other virtues too; but…it is now specially difficult for us to desire — let alone to achieve — complete chastity. In the first place our warped natures, the devils who tempt us, and all the contemporary propaganda for lust, combine to make us feel that the desires we are resisting are so “natural,” so “healthy,” and so reasonable, that it is almost perverse and abnormal to resist them. Poster after poster, film after film, novel after novel, associate the idea of sexual indulgence with the ideas of health, normality, youth, frankness, and good humour. Now this association is a lie. Like all powerful lies, it is based on a truth — the truth, acknowledged above, that sex in itself (apart from the excesses and obsessions that have grown round it) is “normal” and “healthy,” and all the rest of it. The lie consists in the suggestion that any sexual act to which you are tempted at the moment is also healthy and normal. Now this, on any conceivable view, and quite apart from Christianity, must be nonsense. Surrender to all our desires obviously leads to impotence, disease, jealousies, lies, concealment, and everything that is the reverse of health, good humour, and frankness. For any happiness, even in this world, quite a lot of restraint is going to be necessary; so the claim made by every desire, when it is strong, to be healthy and reasonable, counts for nothing. Every sane and civilised man must have some set of principles by which he chooses to reject some of his desires and to permit others. One man does this on Christian principles, another on hygienic principles, another on sociological principles. The real conflict is not between Christianity and “nature,” but between Christian principle and other principles in the control of “nature.” For “nature” (in the sense of natural desire) will have to be controlled anyway, unless you are going to ruin your whole life. The Christian principles are, admittedly, stricter than the others; but then we think you will get help towards obeying them which you will not get towards obeying the others. (emphasis added) 
For any happiness, even in this world, quite a lot of restraint is going to be necessary.
Lewis goes on to write:
We may, indeed, be sure that perfect chastity — like perfect charity — will not be attained by any merely human efforts. You must ask for God’s help. Even when you have done so, it may seem to you for a long time that no help, or less help than you need, is being given. Never mind. After each failure, ask forgiveness, pick yourself up, and try again. Very often what God first helps us towards is not the virtue itself but just this power of always trying again. For however important chastity (or courage, or truthfulness, or any other virtue) may be, this process trains us in habits of the soul which are more important still. It cures our illusions about ourselves and teaches us to depend on God. We learn, on the one hand, that we cannot trust ourselves even in our best moments, and, on the other, that we need not despair even in our worst, for our failures are forgiven. The only fatal thing is to sit down content with anything less than perfection. (emphasis added) 
- Lewis, C. S. Mere Christianity (New York: Book-of-the-Month Club, Inc., 1993), 78-79.
- Ibid, 79.