Celebrity trainer Tony Horton says this is the biggest mistake people make starting an exercise program

Tony Horton is one of the most visible people - if not the most visible person - in all of American fitness.

The credit for that goes to his work creating P90X, the most successful home fitness program of all time.

Horton has created many home exercise programs and led training sessions himself, which gives him a particularly strong understanding of how people react to exercise programs.

We spoke to Tony recently and asked him about the biggest mistake people make when they begin an exercise program.

For Tony, it's all about the journey. And he thinks that the biggest mistake people make has everything to do with thinking about what they expect six months from now instead of focusing on crushing it right now.

Here's what he told us when we asked him about the biggest mistake:

"There's probably 20, but the one that comes to mind is that they have unrealistic expectations. And part B of that is that it's too much based on ego and not health and wellness …. but I think that most people who start workout programs put all their energy on the scale, a tape measure, the reflection in the mirror and the hope that people will say really nice things about how they look in the future."

"And none of that has anything to do with your health, your wellness, your fitness, your durability, your lack of vulnerability to illness and injuries, and that's where you should start. So it's all about prioritizing and purpose, if your purpose is more about 'I wanna do more, feel better, be less vulnerable, be more durable, and actually function well in my own flesh,' then that's a good way to do it."

"And typically it's not the focus on hoping things are going to change down the road as a result of something you're going to do now, so that you look better, and your dress size is smaller, and your belt goes down a few loops, and all that stuff."

"Ultimately I'm trying to create lifestyle programs through food and fitness. The idea here is to focus on being a better person, a more productive person, a less sick person, a better father, mother sister, brother, uncle, aunt, a better employee, someone who says 'yes' to things that are physically or emotionally challenging, as opposed to what they used to do prior to exercising and eating well."