Environment is primary.
Individual will is secondary.
When you use your will, you either escape a toxic environment or create your own. Thus will is really a tool you CAN use to create a positive environment, either a personal mental space or a physical, real-world environment. Most times, will without the resulting environment to support it, fails.
Examples: You escape the toxic one by changing your life circumstances (ie, selling your car and biking to work in order to lose weight). You create your own environment when you buoy yourself along with a positive attitude and motivation towards reaching your goals (ie: you want to lose weight, so you listen to motivational tapes, read motivating books, and join a dieting group).
Either way, you create an environment in which you can succeed. If you are in the correct environment, your chances for success are greater.
The hero stories we hear are inspirational, aren't they? They hold up heroes as ideals, don't they? Kinda convenient how the stories only last two hours, isn't it? Did you know 90 to 95 percent of diets fail to keep the weight off long-term? (I'm just repeating that; I haven't confirmed it.) The point is, your will power alone is not enough to create success unless it results in a positive real-world environment.
I'll assess each combination of will and enviro.
Good environment + no will = moderate chance for success. Still need will to really succeed, otherwise you are coasting along, supported by the environment. Biking to work is a good example, as you are forced by your environment (no car) to pursue your goals, change your habits, etc.
Good enviro + good will = best chance for success.
No enviro support for goals + good will = little chance. You can't breathe without air, you can't swim without water, and you can't lose weight when you are alone at home, hungpy, bored, and faced with a freezer full of ice cream and a cupboard full of Oreos. Mmmmmm, ice cream and Oreos...
no enviro + no will = dur. Only including this category to be thorough.
ALLLLLL sorts of challenges contain both of these elements; environment and will. I propose that the pattern I have established above fits EVERY challenge/problem in life.