I speak about the core philosophy or set of values more. Both people who are generally pessimistic in their world view and typically optimistic can be jolly and grouchy, depending on their mood. I am talking more about their overarching outlook.

The parent comment to my original comment mentioned people who are "fake" optimists. I would describe them as jolly or bubbly often, but ultimately pessimistic. That's why their positivity feels disingenuous. It is a facade or a mask. I appreciate their effort, I am simply drawing a distinction between jolly/grouchy and optimistic/pessimistic.