Do you ever feel like you know exactly what to do (exercise) but when it comes time to execute you can't get yourself to do it?
Researchers have found this to be explainable by a tendency of your brain we have had for millions of years: the conservation of energy.
Over the years conserving energy was vital to human survival. Search for food and shelter, competition for mates, and avoiding risky situations were top priority for anyone alive then.
These processes consume monstrous amounts of calories and any trick or short cut that allowed one to save some of those calories for later decisions were favored in the game of survival. Your brain has this wiring for efficiency built in.
You might notice it when you go to work out and instead find a less demanding distraction to take up your time. TV on the couch for example. Working out is much harder and therefor burns far more calories than sitting on the couch. You know this and so does your brain. But your brain is working in this way you might not be aware of where it seeks the path of least resistance. In ancient times this helped survival, in our times it is killing us faster.
I often talk to people who are frustrated that they can't get motivated to work out. They say things like "I know what I need to do, but when it comes time to do it I cop out and find something easier." Or, "I have to have a place to go to exercise. It has to be different than my home or workplace where I am all day."
These people are frustrated in themselves because they feel like they will never be one of those fitness types. You know, those people who seemingly have endless motivation for time in the gym, cardio, and healthy living. It's not until I explain to them that those fitness people have just as much of an issue staying motivated and that their brains are equally seeking out easier, less energy demanding behavior. So what's the difference between them and you. Those who exercise regularly and those who always find the path of least resistance differ mainly in one category: discipline.
Understanding everyone has a mass between their ears that wants to be lazy helps if that leads you to delegate your exercise choice to routine or habit. Since you know you from your past you won't find the motivation on your own and since making the choice to get sweaty every day is so counterintuitive you should unload that decision to your schedule. That's the place where you get things done whether you feel like it or not.
There is freedom in knowing how your mind ticks. Especially when you've learned that you are not unmotivated, lazy, or doomed because you don't choose to beat your own ass every day with a workout. That actually means your brain is working right - trying to conserve energy.