Mental Mistakes

I made a mental mistake at work on Tuesday.  I miscounted some money which made it look like we were short.  When I discovered the error, it was too late to fix it.  I sent a message to my boss to alert him of the problem and that I would come in Wednesday morning to get it fixed.  He called later and tried to get a better understanding of what took place.  I knew he would not understand what happened because it took me a while to determine exactly what I did to cause the problem.  After my explanation, he went on a tirade about me making another mental mistakes.  He reminded me that my mistakes were becoming more frequent.  He told me to get my head in the game.  That's easier said than done.  My problem is that I participate in so many different games, I have to change jerseys and adapt to a different set of rules 4-5 times a day.  That's enough to wear anyone out mentally and physically.