The subconscious mind is comparable to a conscientious, loyal and hardworking worker. It does not sleep.
It does its job without fail. It is loyal and gives you what you ask for. If you compare it to your conscious mind, you would undoubtedly notice the difference.
The conscious mind is easily tired and is much more limited in its ability and capacity. In contrast, the subsconcious mind is never tired, that is why it never sleep. Its ability and capacity is tremendous, beyond the ken of men.