Sometimes its hard to not feel like a failure especially when everything that you try to do just doesn't work with you at all... You try to think and act positive but something always comes around the corner and bits you in the butt and that's when you start thinking those negative thoughts that you cant do anything right and you will always be a failure or a loser or whatever come into your mind when something you think you did good on but it ends up with bad results (like a test for an example).
Best thing to do is to never give up on yourself no matter what goes on in life. And to get rid those negative people that is not helping you to think differently about yourself out of your life and keep and get better people in your life that does help you think that you are not a failure or anything negative about yourself so it can help you become successful with life.