How do I know to stop and have a break if I have not finished?

think about how your feeling when your doing what ever you are doing. think about how you feel. are you tired? do you need a break? and force yourself on a break to regenerate and regather your emotions, thoughts, and feelings. clear your mind and relaxe even if its only for 15 min. over working yourself on anything can be strussful and actually make it harder to get anything done. overworking yourself can hurt your mental state as well. treat your body like a temple take care of it because its the only one you got. and i dont know the situation your in weather its work or school but this applies in any situation. take care.