You can’t just stop eating french fries and then start eating ice cream. That doesn’t solve the problem. It isn’t enough to stop doing one behavior. You have to replace it with something-substituting the behavior with another, faking it until you make it.
There isn’t a lot of thought put into starting out to become a runner. You put on your shoes and go. It isn’t until you do this for, I don’t know, thirty days or so that you can say you are now a runner. Because you can look at your history with satisfaction.
The point is action is the key to changing behavior. It isn’t what you can’t do, it’s what you now can.