But how can this be true? Surely you get rich by being right?
To be clear, I don't think there's a strong correlation between being rich and being a pessimist/optimist.
And to your original point, being right cannot possibly be biased towards optimism or pessimism. Any apparent correlation is more of a reflection on what everyone else thinks... and they are wrong! Cheers to being right!
I do think pessimists, especially of the depressive variety generally do not get rich. The reason is that getting rich is hard, everyone nominally wants it, so it’s highly competitive and there are no easy paths. To find a path generally you have to take an action that almost by definition is low probability of success. You don’t have to be a beaming cheerleader to make this happen, but being an eyore is most likely disqualifying.
Perhaps there is something to the saying ignorance is bliss.
I also think depressed people would regress to the average if they weren't depressed. It's not a sustainable way to think harder and open your eyes to the world around you.
Starting with an accurate world model, no matter how dispiriting, seems to be a prerequisite for knowing the most effective action to take.