A pessimist is a fellow who lives with an optimist.怎么翻译

英语翻译
Whether you are an optimist or a pessimist has a lot to do with genes.But the way you are raised and the effort you yourself put into building your levels of optimism also make a difference.Sandy recommends that you "act first and the right feelings will follow".
"People can learn to be more optimistic by acting as if they were more optimistic," wrote Sandy in her book,Breaking Murphy's Law.She suggested this would stop one from giving up after every single little failure."You might succeed more than you expected," she wrote.
Focus on the things that you can control instead of worrying about possible failures.Try to see the good aspects in every situation; even if you are just mopping the floor,take time to stand back and admire how shiny and clean the floor looks when you are done.Hang around with optimistic and cheerful people,and they will help you see the brighter side of life.

英语翻译
“An optimist sees the rose; a pessimist the thorn.” Aristotle once said.

I'm not just being a pessimist.这句话怎么理解,be being 这个结构在句中起什么作用呢?
主要是想知道be being 这个结构在句中起什么作用呢？
它与I'm not just a pessimist.有什么区别？