In our society, all we do is think about the future. We are excited about upcoming events, nervous about conflicts/challenges, and we never stay in the present. Despite this reality, Meursault does the opposite. He does not think ahead and he does not worry about the future. Instead, Meursault lives in the moment and accepts his reality.
Due to his mindset, Meursault is able to enjoy the little things. He was able to enjoy a day at the beach with Marie, not thinking about anything other than her. At an even larger scale, Meursault was able to become content with prison. While the situation to anyone else would be horrible, Meursault finds the good in it and does not resent his situation.
To outsiders, Meursault is a sociopath. He is apathetic and has no drive for anything in his life. He is someone no one hopes to become. However, when his actions are closely analyzed and his mindset is understood, he is living life at its simplest and seems to have it all figured out.
He does not worry and is not filled with jealousy. Most importantly, he does not do anything he does not want to do. He lives without regrets. While everyone else is caught up in past problems and future dilemmas, Meursault is living life as intended. Above anyone else, he is a free man.