Pessimism is easy. Anyone can come up with a risk, a downside, or a way things could go wrong.
Optimism, on the other hand, is hard. The optimist sticks their neck out for an idea. They try and imagine the best version of the future, even if that future looks far away or tough to achieve. And they work hard to convince others of their vision.
I think it is worth defaulting to optimism where we let ideas and possibilities flow. There’ll always either be time, or others, willing to offer a different perspective.