Optimism is cowardice. Best case, they meant something different: energetic, positive, confident.
In my interpretation of the words, I tend to think of optimism as being the brave thing because having hope is more difficult, and IME, you can only muster energy to solve a problem if hope exists. Conversely, pessimism to me feels cheap and easy, and if you say "everything's fucked, what's the point" then nothing gets solved
So, it's probably more of a quadrant/compass along the axes of optimism/pessimism and proactive/passive
Knowing you can solve it doesn't mean you assume it'll get solved without effort.
It just means you're confident the problems will get solved. Pessimism stems from a perceived lack of control in my experience.