Optimism is an expression of positivity. It’s about seeing things in the best way possible and expecting the best things to happen. An important clarification to make is that it is not about being overly idealistic. Everything has positive and negative elements built into it, and being optimistic is choosing to focus on the positive elements and expecting those to prevail.
Ultimately, when you’re optimistic you have an overall belief that good defeats evil in this world. You can find evidence for that in seeing how one particle of light can undo millions of particles of dark. Or think about this Vedic principle that monks adopt - For every word of gossip or negativity they speak about someone they are required to say 10 positive things.
You’ve heard this before in the expression “The glass is half full”. If we break this down, we’ll see that this is just a perspective and a choice against the alternative “The glass is half empty”. It’s all about seeing the positivity and possibility in the situation, which is your decision to believe that good beats evil in this world.
I think this concept of optimism is articulated very well in a Winston Churchill quote that goes as follows, "A sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty.”