Being optimistic for no reason is a recipe for disaster, because optimism is always at odds with human stupidity.
If you want to be optimistic (which is desirable), you should shape your environment to promote optimism: most often, this is done by diversifying your portfolio and/or creating optionality so that your environment is sufficiently hedged against stupidity.
A very practical example: investing in index funds rather than trying to outsmart the market.
At the same time, you should also be conscious that Optionality can hinder risk-taking.