We are so often under the illusion that one day we'll find happiness; that one distant thing, laying in wait to fix all our problems. Then when it finally comes, we realize our lives have not changed, we are not all that different and our hunger for contentedness is not satiated.
Longing for that which we do not have, is it a motivation? Is it a crutch? To feel we have achieved something, when we finally reach Time A, or completion of Task 1. The potential to feel this, either propels us into action or leaves us feeling undeservedly accomplished when the time comes or the task is complete.
Then, when we've finally hit our mark; we've made it to the goal...we're left longing for a time passed, that we cannot get back and we've overlooked while it blurred by in our peripheral. We're left, longing again for something we do not have; but this time we cannot have it. Only in memories can we access that time that we so ignorantly sped through.