It’s a common fear of people that being optimistic makes them miss things that could go wrong and therefore make the ship sink. If you think nothing will ever go wrong you’re not optimistic but delusional. Good strategy means you are prepared for the great to happen as well.
Having said that the opposite is also possible: while most of us have thought lots of times what could go wrong about the various things we do, what if there are unexpected blessings? Could we capitalize on those? Let’s say your website would suddenly get 5 times more traffic or your public speech was so well received that people wanted all kinds of things from you afterwards. Are you prepared for that? Do you have the time if someone suddenly offered to help you make your dream come true?