I think that a case can be made that Michael was unsuccessful. Michael believed that life owed him more than towards what he worked. He sensed that he was destined for something more than what he was. In the end, he believed himself to be better than his marriage and his friends and that what was truly worthy of him awaited from the inward definition of both realms.
He has to be seen as somewhat unsuccessful because what he believed about life did not materialize. He ends up losing his marriage, some aspect of his freedom, and his social standing because of his "impulse." This impulsive action did not result in liberation or a new conception of self. When Michael envisions that stealing the razor kit is an affirmation of some type, it is not. He is unsuccessful in embarking on a misguided mission of self- definition. He is unsuccessful in trying to talk his way out of the transgression with store officials and police officials. Even in jail, when he should be confronting the harsh reality in front of him, he is unsuccessful in being able to do so, reverting to childhood memories as opposed to anything substantive. In the context of the entire story, Michael has to be seen as unsuccessful as there is little in the story's ending to show he has been successful.