You decide to yourself if you are successful or not. That is my own opinion.
You are the one who can decide if you are really successful or not. For example, you won a chess match against your classmate. Even if you won against you classmate, if you are not happy with it, then, it is not success. Say, there was a test. Your mission is to ace the test. You forgot about the mission and you were not able to study before the test. Now, you decided to cheat. After the test, the test papers were checked, soon, you realized that YOU GOT A PERFECT SCORE!!! But, in the end, despite that PERFECT SCORE, you do not feel that you are great, you feel uneasy, therefore, even if you got that perfect score and completed the mission, you did not achieve success for you did not feel success at all. That is just my own opinion. Hope it helps! :)