Staying positive is important, but a lot of us are oblivious to the very real downside of obsessive enthusiasm – optimism bias.
The city of Chicago had a big problem. Street trash was everywhere. So the city came up with a brilliant plan: start paying everyday people to collect street trash. But crafty citizens started gathering trash from one neighborhood, then quietly depositing it in another. They had inadvertently incentivized people to drive around the city, moving trash from one place to another.