Desire leads to the gratification of desire, which in turn leads to the repetition of the gratification. Repeated gratification in turn leads to the formation of an intensely pleasurable habit, one that persists even after the desire wanes and disappears, the very desire without whose gratification the habit wouldn't exist in the first place. Memories of pleasure conspire in the maintenance of habit. The ancient rake, exhausted and infirm, is not up for another round of debauchery, but the memories haunt him, of pleasures past. The memories keep alive the habit after the desire has fled the decrepit body that refuses to serve as an engine of pleasure.
And that puts me in mind of Schopenhauer's advice. "Abandon your vices before they abandon you."
When one is in the grip of a desire one typically knows it. He who wants a cold beer on a hot day knows what he wants and is likely to deem unhinged anyone with the temerity to deny that there are desires. Anywhere on the scale from velleity to craving, but especially at the craving end, there is a qualitative character to desire that makes it phenomenologically undeniable. If the beer example doesn't move you, think of lust. Lust is an intentional state: one cannot lust unless one lusts after someone or something. But although lust flees itself, voids itself in a rush towards its object — as Sartre might have said — there is nonetheless something 'it is like' (T. Nagel) to be in the state of lust. In this respect, desire is more like the non-intentional state of pain than it is like the intentional state of belief. There is most decidedly something it is like for me to desire X; but what is is like for me to believe that you desire X? Is it like anything? Not so clear.
What is idolatry? I suggest that the essence of idolatry lies in the illicit absolutizing of the relative. A finite good becomes an idol when it is treated as if it were an infinite good, i.e., one capable of satisfying our infinite desire. But is our desire infinite? That our desire is infinite is shown by the fact that it is never satisfied by any finite object or series of finite objects. Not even an infinite series of finite objects could satisfy it since what we really want is not an endless series of finite satisfactions -- say a different black-eyed virgin every night as in popular Islam's depiction of paradise — but a satisfaction in which one could finally rest. "Our hearts are restless until they rest in Thee." (Augustine) What we really want, though we don't know it, is the absolute good which is goodness itself, namely God. This idea is common to Plato, Augustine, Malebranche, and Simone Weil.