Every day I have a handful of reasons why I shouldn't exercise: I'm tired. Something hurts. I worked out too hard yesterday. I deserve a day off. I have too much to do today. I also run into mind games while actually out exercising: You can't run that far. That's too much weight to lift, it's too difficult. You really are too tired to push yourself that hard. During the most difficult race I ever participated in, and that I was completely untrained for, this is what my mind was saying to me: You could walk and no one would know the difference. Why the heck do you put yourself through this? What are you doing? This is stupid. You'll never finish this.
No! No! and No!
I finished that race, and felt good for doing so. Your brain is lying to you, and will play tricks on you. Yes, you can do it! Yes, you need to do it! Yes, it does matter! Yes, someone will know the difference - you will. I would way rather push through and have a sense of accomplishment than not do it and feel guilty. Don't listen to your brain, it will lie to you every time.
