Nothing is impossible denies the existence of things that are impossible, by claiming that everything is possible. That is to say, even for things that seem unlikely or bound to fail, there are chances for them to become likely or successful. Impossible means the chances to fail is 100%. So nothing is impossible means nothing is 100% bound to failure. In such a sense, nothing is impossible is kind of a conceited declaration.
Impossible is nothing believes that the thing that seems impossible “is not a fact but an opinion.” “Impossible is just a big word thrown around by small men who find it easier to live in the world they've been given than to explore the power they have to change it.” If we say Nothing is impossible is a ‘declaration’, then impossible is nothing is a ‘dare’. The latter conveys the courage and confidence: even for things that may be 100% bound to failure, I am not at all afraid and I regard the possibility to fail as a thing of no account, utterly insignificant, because “Impossible is potential. Impossible is temporary. Impossible is nothing.”