We need rules and guidelines in society. We need to drive at or under (or...at least close to) the speed limit. When a traffic light malfunctions, the intersection becomes a four-way stop.
Even when we're not talking about laws, our actions are guided by rules--tacit or otherwise. If we eat dinner at a fancy restaurant, it is generally frowned upon to remain at the table for hours after finishing your meal.
You might even feel like there are rules when you're running--but you don't have to feel that way. Nina Kuscik, the first woman to officially win the Boston Marathon, puts it like this:
"Running gives you freedom. . . You can go where you want and think your own thoughts. Nobody has any claim on you."
Running can be as free as you want it to be. Nobody has any claim on you. You might have a plan for how you want to run each day--and sometimes that plan can feel a little constraining--but it is your plan. It's your choice to follow it to the letter, or let it go for a day.
Ultimately, there is a time and place for both. Sometimes you have to dig deep and complete the workout you planned as planned. But, sometimes, the best thing for mind and body is just run you how feel, for as long as you feel like going. At least for that day.