"The bottom line is that a person who wants to remain ignorant of the money-making side of business will never hold power. Employment is the opposite of freedom."
I also agree with a timer method, one of which uses a kitchen timer (Pomodoro). You commit yourself to nothing else for 15 minutes, and stop immediately once the timer goes off. You'll find yourself adding intervals once you train your focus back to longer hours.
Also, proper nutrition and hydration is very important (good one, Mz).
Best of Luck!