No, being a pessimist does not equal being a realist.
Realists try to gauge life as it really is and attempt to be objective about their conclusions. Pessimists always have a bias for misfortune and hardship. Realists are honest and pessimists lack hope.
Leading a conservative life tends to keep you in a comfort zone, but without risk and testing the contours of what is possible, there is never any room to think big and make dreams come true.
People with a generous helping of imagination mixed in with healthy dose of common sense are the ones who challenge what is achievable and change the world for the better.