Reason is an interesting concept. As my friend pointed out over coffee not too long ago , its devotees insist that it operates on the basis of neutral, hard facts, even though the point from which their deductions start is an absolute and unshakable belief in its existence. Although you can rationalise, in the logical and consequential sense, from one given point to another, the point of departure itself - the founding principle - is always a leap of faith.
I think life is like that. All of us - psychotics and paranoics included - can see logical chains which put the pieces of the world together in a way that makes sense. Just look at the narratives we construct to explain every aspect of our lives, from love to ideology. But just because it makes sense does not mean it is true (or, even that it is the best possible lie). Start looking at things from a positive perspective and the logic that follows will weave threads of harmony: if your starting place, by contrast, is cynicism, then the world you logically invent is permeated by pettiness, hypocrisy and manipulation.
A good example of what happens when we believe our own rationalisations are true or worthwhile simply because they make sense is illustrated by GK Chesterton in his book 'Orthodoxy'. The madman, he says, has an explanation for everything, yet "his mind moves in a perfect but narrow circle. A small circle is quite as infinite as a large circle, but, though it is quite as infinite, it is not so large...There is such a thing as a narrow universality; there is such a thing as a small and cramped eternity...when this kindly world all round the man has been blackened out like a lie; when friends fade into ghosts, and the foundations of the world fail; then...the man, believing in nothing and in no man, is alone in his own nightmare".
If we predicate life on an understanding that is too narrow, egotistical, material or inhumane we cannot see beauty or understand virtue. We will simply see what our minds conceive, reflected back at us. It is only if we live, as Kant advised, to pursue perfection in ourselves and happiness for others, that the world can come to ressemble our best conceptions.