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.

Perhaps the biggest reason that millions upon millions of people begin fitness programs is to lose weight. And of course most programs, including P90X, come with a comprehensive diet regimen to accompany the fitness portion.

It was natural then, when we spoke to Tony recently, to ask him what he's noticed is the toughest thing for people who are starting a program to lose weight.

To him, it's all about inflated expectations and not living in the now.

Here is what he told us:

"The discipline of it. Being consistent with it. The expectations of how quickly things are gong to change for them. That's the reason why most people stop in the first or second week, because it didn’t happen overnight.

"I created the program to be 90 days — they’re all 90-day programs because sometimes, for a lot of people, they have a different starting point. If you have 125 pounds to lose and you’re 42 years old, you’re at a really different starting point than a 27-year-old ex-gymnast who has 9 pounds to lose.

"So you have to kind of be ok with the process. Being ok having to modify, being ok with not being able to do a lot of the exercises initially. It’s not like anybody says ‘I want to climb Mt Everest’ and just straps on their gear and goes, you know, there’s a lot of steps between that thought and ending up on the summit, and losing weight and getting fit is the same thing."

We also asked Tony what he would advise people to focus on instead of getting fixated on the result of the weight loss and how they would look:

"… My advice to people would be — take it slow. It’s an ebb and flow, you’re going to have good days and you’re going to have bad days, you’re going to feel strong, you’re going to feel weak. Pass your expectations, stop thinking about how you hope to look in the future and just kind of stay present.

"My expression is ‘do your best and forget the rest.’ I’ve said it about 18 trillion times, and that’s what that is, that’s all that really is. Doing your best means showing up, being in the room and seeing what happens and not expecting the same performance that you did 20 years ago or that somebody else you know has done. It’s ever changing and being ok with reality. Reality is that thing that’s actually happening to you and if you can’t deal with that you’re always going to struggle."