If everybody were such a pessimist, we'd never try to improve anything because there's a risk it might not always work or need adjustment in the future.
And a certain someone would also be there telling everyone not to go outside of the cave because there's tigers :)
If everybody was such an optimist... well, they would eventually become pessimists when they realized good intentions alone aren't enough, but there are few optimists with good plans.
Ok, there are also very few pessimists with good plans, but I didn't mean to turn you into a pessimist now ;)
And a certain someone would also be there telling everyone not to go outside of the cave because there's tigers :)