Of course you need to believe in yourself. But Tomic is not a teen anymore, he should know better than to say things like that in public. That´s the difference, it would be smart to keep a little lower profile in public, even if you have an enormous self-confidence.
I think he's not in that kind of perfectionistic details at the moment, he may try to improve his communication later in his carreer (as it happened for Murray and Djokovic who changed their communication even if they were much better than him from the beginning), but he has so many problems in the Australian media at the moment, not related to that
... and problems with his tennis, and with the Australian law