What is Optimism in simple words?

Could you please explain what Optimism means in plain English? I'm trying to grasp the concept but I find it a bit abstract. Could you break it down into something easier to understand? What does being optimistic actually mean in our daily lives? How does it differ from being pessimistic? And why is it important to cultivate a positive, optimistic attitude? I'm curious to know how this mindset can impact our decisions and outlook on life.