There's a catch-22 nature to addiction and/or looking too forward: something has to be really good for it to be looked forward to too much. By striving to find transcendent experience one is unwittingly striving to find addiction. You can't really have one without the other, it would seem. Drug addicts have found the most obvious and seemingly dependable source of pleasurable experiences while simultaneously finding the most addictive and destructive. And, of course, the thrill wears off even as the need for the the substance doesn't.
I suspect one reason to not to look forward so much is because by definition you're not living in the moment. By definition you are, in a sense, "wishing your life away" and we know how precious life is. It's not particularly helpful or conducive to gratitude, to be bummed that it's Monday instead of Friday, say, and gratitude is arguably the mark of true religion.
Happened across a Psychology Today link:
The circuitry connecting the orbitofrontal cortex and ventral striatum is a beautifully crafted machine for learning what you like and pursuing it with single-minded purpose. Its fuel is dopamine. And this machine sends messages directly to the premotor and motor cortex. It guides behavior, action, in pursuit of the good things in life...We can learn to go after anything, full bore, if it attracts us. And that's how we get ahead in life.
But it's also how we get addicted. The goal-pursuit circuit is a bit too flexible. Cocaine high. Oh yeah. That feels good. Want more. Got to get it. That drink at the end of the day. Feels good. Want it. Stop at the liquor store on the way home. These tendencies eventually cause us a lot of suffering, but they are simply byproducts of a brain that evolved to seek rewards, based on their attractiveness, and to pursue them with almost relentless energy.
When your back-ache gets bad enough, you start doing physio or yoga, so that you can use your upright spine to its best advantage. When your addiction gets bad enough, you'd best figure out how to use the goal-pursuit circuit for what it's designed for: to be successful and happy, to avoid suffering, and—of course—to feed the little ones back at the cave.