I choose to fill my mind with positive, nurturing thoughts.

Thoughts don't arrive by invitation, which is why trying to select them one by one tends to backfire.

Input is a different matter. What is on the screen at half past eleven at night is a genuine choice, and one of the few available in the vicinity. So is who you read, what plays in the car, whether the last thing before sleep is an argument between strangers.

The mind works with the materials lying around the room. You cannot choose what it makes out of them. You have a surprising amount of say over what you leave out for it.