The Midrash Shmuel explains that this alludes to a person who awakens to reality late in life. The night is a reference to a time in life when a person is older and has less strength, if he is awakened at that point to the reality of the world, he has done himself a disservice. If a person only realizes later in life that there is much more to this world than the physical life we live, that we are here for a purpose in life and not just to enjoy physical pleasures, he will realize that he needs to change his whole way of thinking and living. At this stage it becomes very difficult to make changes because a person not only has a way of life so ingrained but they simply lack the physical strength to make the necessary changes. Although it is always possible to change nevertheless his lack of awareness until his old age resulted in a great disservice to himself.