When I first started working with a personal trainer, the word can't slipped out a lot! Some of the crazy stuff they ask me to do is like way out there! Stuff I never thought I would be able to do. But what I've learned, besides saying you can't do something to your trainer gets you extra burpees, is my trainers know my capabilities better than I do.
Sometimes we are our worst enemy at telling ourselves we can't do something. And the worst part is we tend to listen to ourselves. There are times it takes the trainer proving me wrong, but I end up being able to do what they ask of me. So, when you encounter something difficult or out of your comfort zone, don't tell yourself you can't do it. Keep positive, stay focused, and know you can do anything you set your mind to!