When I say that New York can be a bad influence on a investor due negativity, perhaps I can explain myself better.
I'm sure people there are plenty positive, maybe even average relative to other cities. Perhaps even the numbers show that they own plenty of stocks. But they are also known as having big egos, especially people on Wall Street. When you have that big ego you can talk yourself into selling positions (like Eckhardt says its already a natural tendency for people), you can talk yourself into shorting some stocks (because you think you are so much smarter than everyone else, like Ackman on HLF), you can talk yourself into trading in and out of positions. The latter is pretty much the business model of most hedge funds (which are usually located in NY).
So even if the people themselves are positive, they are lead to BEHAVE as if they were pessimists. Kinda like my mistake on Ethereum, I was positive on it but BEHAVED as if I was negative when I took profits too quick and used a too close of a trailing stop, actions matter more than intentions.
From my observations, I just happen to think that NY (the city, the books, the media and all the culture that comes from Wall Street) will lead people to behave in ways that hurt convexity (be it because of transaction costs, selling winners too soon, shorting selling, being out of stocks because they are "too high", being a contrarian etc), so even people that are optimistic will behave in ways that are pessmistic and are anti-convexity
A lot of the people influenced by NY get saved by Warren Buffett, that's what helps to 'balance' them back and increase their optimistic behaviors. They read about him, watch interviews, etc and end up learning the folly of the ego approach of thinking you can outsmart your way to exponential profits through high turn over, shorting, selling positions because of 'brilhant' valuation research, etc. As a result, they become better investors
This might just be the greatest achievement that Buffett ever pulled. He saved so much people from anti-convexity nonsense