That's where we started, and it's where we now end.
Are we products of our environment? Or do we get to determine who we are?
Yes. Yes to both.
Your Environment (capital E - meaning the physical and social environments around you, the environment of your physical body and health, your internal psychological environment, all of it) is always going to shape you. However, you have the power to act on that Environment.
As such, you have the power to author who you are, and who you will be. But to do it effectively, you have to let go of the idea that it's as simple as a decision.
The reason people have trouble losing weight, the reason they get so frustrated by it, is because they're trying to start a fire while standing in water. We are convinced that failure is a function of flaws, that if we can't accomplish something it's because of our own personal weaknesses.
If you are overweight, it's probably because your Environment made it easy for you to become that way. If you struggle with losing weight, it's probably because that Environment is fighting you.
And It may, in theory, be possible to overcome that Environment by sheer force of will, but isn't that demanding too much of yourself?
It may, in theory, be possible to start a fire with damp wood on wet ground. But if you tried it, you'd just wind up frustrated and dejected.
This isn't a quick fix. It's difficult*, and anyone that tries to tell you otherwise probably has something to sell. But it can be done. And you know what?
It's worth it.
*Believe me, I know it is.