The road to success has curves, hills, rocks, and then you reach your destination. However would you travel anywhere without proper preparation? Say on an empty tank? No oil? Flat tire? Or would you stop in the middle of flowing traffic without cause? How would you reach your destination.
This applies to exercise, or any goals you are trying to reach.
I am applying this metaphor to workouts. You must have proper fuel to workout (nutrition / fuel). You must balance your carbohydrates and fats (oil). You must have adequate sleep (flat tire), and to get results of any workout you must follow the specifics be it a calendar or and a trainer (stopping in the flow of traffic).
Know Your Limits, I have to remind myself with each workout my limits and you too should do the same.