Have you ever heard someone near you say "light weight" under their breath before they take a lift? Training your brain is more than just telling yourself "I can do it." Brain training and becoming "mentally tough" is just as essential as physical training. If you can't get your head in the game, your thoughts become the thing holding you back.
However you focus when you start your work out (or tomorrow's Lift Off), it's your ability to shift out of a dark mental cave that can keep you going when pure will power isn't enough motivation. This is where self talk and other focus techniques keep you in the game. On the flip side, you can have a day where your mental fortitude takes pounds off your lift or can be the difference between sprinting that last 200m instead of jogging in defeated.
But just like anything else worth doing, developing the ability to refocus and reign in negative thoughts takes practice. Brain training can consist of something as simple as telling yourself - "I am here to have fun," "I only have __ left," or even "just stop thinking and go." Sure there are days you won't be able to overcome a bad day or a workout freak-out, but the important thing is to show up and try. Let the bad thoughts come and flow through you like water. With practice, you will start to use you the negativity to fuel the workout and refocus. Next time you are in the gym, don't discount the power of your frame of mind. Train your brain and let your mental state work for you from the moment you walk into the room until the moment your judge says "down."