Fully Functioning

I have done pretty good this week with the routine and making progress on most areas. By Friday though, the tank was empty and I just couldn't be bothered maintaining the effort. I really do wonder how some people operate at full functionality all the time. I know that when I'm motivated, I can achieve truly amazing things - but my ability to stay motivated and function at that level is severely restricted. How do I improve my ability to become fully functional most of the time?