You're not always as tired as you think you are. There is a difference between being genuinely fatigued, overwhelmed and simply not in state to do the task at hand. If you are genuinely fatigued having rest should make you feel amazing once you've had it. If you're overwhelmed you're expecting too much to be done in too little time and need to break the task up into smaller parts to get the job done. However, many people feel tired when actually they're simply not in state to do the job at hand defined by having rest not feeling refreshed for having it and feeling worse for not doing what you would promised yourself you would do. You didn't need the rest you needed better state which you get by starting the job. If you habitually don't want to do what you have to do then you don't actually want the goal you're working towards as bad as you think you do. It's more something you think you should be doing.