Appreciate what you have, for all that you have was once among that which you desired. Appreciation requires this thought, to dispel the endless cycle of desire. Desire is to exist one step ahead of oneself in the pursuit of something; appreciation is to take pause in the present.
The future is unpredictable and the past is a mist, so the present is all we can actually know. To sacrifice the present for an unrealized actuality, or deny it for some past misery, is to ignore the sacred gift given us by the very fact of our conscious being.
Even painful moments (tooth ache!) are of this sanctity, when they are here. For, short of the worst suffering, we can endure anything, find the good in anything, and would be wise to remember this. There is a lesson to learn even in our pain, so trying to escape it is only to delay that suffering, not to deal with it. It is worth holding on. It is worth having hope. If nothing else, we have at least our now, with its multitude of lessons to be learned and joys to be experienced.
It will come, but it will go, it will seem forever, but nothing lasts. It will rain, the sun will shine, who knows which, learn to appreciate both, or else live in unfulfilled expectation.