If you are a tournament player, shaking off a loss will be one of the biggest hurdles that you need to jump.  This entire article can be summed up in 1 sentence…
 
Stop the excuses, admit you lost.  
 
After admitting to yourself that you lost that match and it was your fault, you will then be able to clearly think why you lost and you will learn from your mistakes.  If you continue to make excuses, then you won’t change, you won’t improve, and you will keep losing.