Pessimism and optimisms are both frameworks to assess the world and arrive at solutions or conclusions.
Considering the above image, the pessimist would observe that the people are working harder than they have to while the optimist would observe that at least they are working together – both frameworks allow for solutions to make the work easier and more efficient, or at least less onerous, be identified.
Being positive or negative in your outlook is a modifier to the either framework of pessimism or optimism, not merely (or even at all) different words to describe the same thing. Both outlooks are potential inhibitors to solutions when they serve to merely validate either making the best of the situation or accepting the inability to change the situation. Six of one and a half dozen of the other.
To be negative or positive is, depending on the framework employed, a change resistance mechanism, both of which are maladaptive outlooks when employed to obstruct changing a situation and instead serve to reinforce the status quo, and adaptive outlooks when balanced within the apparently opposing framework.
Being a positive pessimist is to recognize the pitfalls and yet expect better outcomes; which is comparable to a negative optimist, which is to hope for the best, but plan for the possibility of less than desirable outcomes. Both of these positions are compatible with each other and both comprise a realist, flexible and resilient outlook based on experience and probability.
However, being a negative pessimist or a positive optimist are both unrealistic, in that each respectively expects and plans for only the extreme poor or successful outcomes, with little contingency planning or resiliency to consider or recover from unexpected outcomes. Neither of these positional frameworks allow for risk assessment based on experience or probability, but rather wishful thinking or self-fulfilling doom soothing.
The Positive Pessimist and the Negative Optimist have balanced their outlook and framework in an adaptive manner that enhances functioning and the Negative Pessimist and Positive Optimist are maladapted and engaged in confirmation bias and unable to adapt to situations that are outside of their incestuous outlook/framework.
Life has a ying yang functionality while purity of any kind gums up the machinery.