While long term optimism is a force multiplier, short term pessimism is the key to success. This is the exact reason why you see people at "successful" startup

While long term optimism is a force multiplier, short term pessimism is the key to success. This is the exact reason why you see people at "successful" startups/companies jump to very early startups (pre-product/market fit) and completely flounder. The stage between pre-product/market fit and product/market fit is completely different. The usual thing that happens is that these "successful" people have survivor bias and end up wrecking the company they jump to.