The difference between ‘I CAN’T miss a workout’, versus ‘I DON’T miss workouts’ seems trivial. However, studies have shown a 70% difference in people’s actual follow-thru based on this difference in words.
Saying you can (or can’t) implies an external force declaring that you should or shouldn’t do something. When you do (or don’t) you’re making a statement about the kind of person you are.
And the strongest force in our personality is the need to be consistent with the kind of person we’ve decided we are.