What is the meaning of : no pessimist ever discovered the secret of the stars or sailed to an uncharted land or opened a new doorway for the human spirit

it is impossible for someone who is pessimistic/negative to achieve greatness that exceeds what we already know because they can't see the possibility of something great happening and never aim for anything with a chance of failure because if there is a chance they believe it will be the outcome.

I believe it means that a negative person would not make an achievement or something not yet discovered because of the negativity in his soul.