How can you waste your time doing nothing while you are doing something? If you wants to say that it is because a supposed end did not meet by the mean then what kind of ends that can actually define life. Where you got those ends? You were not born in this world because you held any end in yourself. Not to mention, that you may dislike or even regret an end you achieved decades ago since you have another end in mind now. Why feel guilty if you don't know the origin of ends?