You are a liar!
You will have more conversations with yourself than with anyone else in your lifetime.  And I want to challenge you to prove to me that you are not a liar ( at least sometimes) when you talk to yourself.

For example, you’re about to skip the gym, again.

At that moment, you might be telling yourself...

"It doesn’t matter anyway."
"I’ll never get to where I want to be.”
"I will never change and be a person that goes to the gym consistently."

In THAT moment, I want you to identify the lie that you are telling yourself.  The statement that does not feel helpful to you. I want you to ask yourself one critical question.

Is that true?

Let’s say the thought you chose is “I’m never going to get to the level of strength I want to be at.”

Is that true? Do I know for sure that’s true? Is there ANY evidence indicating that it isn't true?

Maybe it is possible that you can get as strong as you want,

Maybe there is a world where you can make this change.

Maybe you need to settle on a neutral statement, like "I don't know with 100% certainty that this thought is true." and see where your brain goes from there. 
Listen and learn more.