T
his will be a short post, to introduce some themes I intend to explore later.
Things which tend to keep existing are more likely to exist in the future. Things which do not tend to keep existing are unlikely to do so for very long. In more complex things, we call tendencies like these desires—what a desire is, is the tendency to do something. 
In even more complex things, like rational animals, desire can take on correspondingly complex forms, even desire of the impossible. Nonetheless, at its core, desire is an expression of a tendency to act in a particular way, especially given the opportunity to do so. The most basic of desires, of tendencies, is to keep on existing. The price of existence is love of existence.
By the same token, suffering is the expression of losing existence. The experience of suffering is to get us to recoil from that which would defray our existence, which we love. This love is not a "trick" of evolution, or a stumbling block to rational thought—it is the basis of all things, the price to be paid for being or thinking at all. Existence and non-existence are not symmetrical—one is love; the other is nothing at all.
Because human beings are complex, and the tools we use to sustain ourselves are correspondingly complex, there is a great deal of room for error in our reasoning. Fortunately (depending on perspective), errors of this sort do not express a love of existence, and consequently cannot be expected to last very long.