An excellent point. On the extreme end, some cultures still practice arranged marriages, and yet the couples are often quite happy. When two people are together for a long time, they tend to become more like each other, to the point where the line dividing them begins to blur. It's an interesting thought that mayb a lot of divorces are ppl bailing out at the first sign of trouble instead of sticking things out and coming out with an even stronger relationship - I don't know why I had never thought of that b4...
I agree, the chances of meeting someone and already being perfect for each other is slim to nil. However, two people that are caring and willing to change a little for the sake of the other can become perfect for each other. For example, there were many things b/w me and my LTR that one of us had an interest in but not the other. Now, as we approach the 18 month mark, the number of such things has dwindled significantly. We've learned to pick up very subtle signals from each other, and to avoid things the other dislikes.
Sometimes two people in a relationship just won't work out, no matter how hard they try. Other times, however, two people can grow so close that they cease to be two separate people and instead become a single entity greater than the sum of its parts, and when this happens, it's one of the most wonderful and beautiful things in the world.