Ray Palmer isn't actually optimistic. It's all a show he puts on for his dead finance. Before he actually was very genuine about it. But that all changed the day Anna died. For weeks, he stayed in his room sulking, refusing to come out for anything. Not even to eat.
In this time, Ray was actually very pessimistic and brooding. Because what was the point of life if you couldn't live it with the ones you love?
Then, one day, after a particularly long chat with his brother, Ray had an epiphany. Anna wouldn't want him laying around being a depressed mess all day. So, he immediately got to work on the Atom suit. He went out of his way to put on the cheery face we know and love today, even when he didn't feel like it. Even when he had relapses in his grief.

Because I refuse to believe he's mentally sane after loosing the love of his life.