My high school gymnastics coach prohibited us from ever saying "can't."
She knew that if we said we can't do something, we immediately set a limit for ourselves. The only way to break through is to tell yourself you CAN do it. Close your eyes and see it happen.
Your brain and your body believe what you tell it.
This goes for all kinds of self-talk.
It all matters and it all shapes your reality.
If you catch yourself saying "I can't...," try pausing to rephrase. Focus on what you CAN do today. Free yourself from limiting thoughts.
Some yoga examples:
Instead of: "I can't touch my toes,"
try: "I can bend my knees to reach my toes to help increase my flexibility."
Instead of: "I can't do Crow Pose,"
try: "I can work on building strength in my core and shoulders in order to lift my feet in Crow someday!"
See how the first version is definitive, conclusive. The door is closed.
Open the door for yourself!