That's clicheed bollocks. Pessimists seal their own fate. They miss out on opportunities to make their world better cos no one in their right mind would want a 'can't be doner' anywhere near anything that matters.
Avoid like the plague. They drain morale and eat time and deter others from getting involved. Embittered types get the solo roles. And rightly so. They're hell to work with.
Some might do. But no two pessimists are the same. I'm not telling anybody not to do anything and I'm not detering anybody from getting in involved in whatever they want either. As I seem to have to continually repeat. Nor do I think things can't be made better. History has proved time and time again that they can. But you have to distinguish between situations where those who wanted what most on here would regard as positive change were in the ascendency, and situations where they're not. We have been in the latter situation for a long time. Personally, I think it's a terminal decline and 'the left' and the working class movement is now doomed to forever fight defensive battles (I also concede that I might be wrong, but I doubt it.)
Being pessimistic, especially about things which are beyond your control, doesn't mean you're embittered. I've known a few embittered politicos who cling on to their political optimism with little or no recognition that what's embittered them is reality letting them down time and time again. (It always will-and that applies to all of us, no matter what your political outlook.) Optimists do have their place, but all that the head-in-the-sand political optimism on display on here will result in is more disappointment due to highly unfavourable wider circumstances that none of us, pessimistic or not, can do anything about. Yes, there is plenty going on, and, yes, plenty of people are angry, but there will be no political breakthroughs, hence what few victories there might be will be only temporary and of a purely defensive nature. Few people will recognise it however, which is why they're doomed to make the same mistakes over and over.
Anyway, you just carry on with what you're doing. Don't let me stop you.