According to Osho, there’s hardly any difference: the optimist believes this is the best of all possible worlds, while the pessimist dreads that this might be true. Both are mirror-image attitudes of the mind; rather than clinging to either hope or fear, he hints at meeting life as it is, with clear awareness.
An optimist says this world is the best; a pessimist gets scared that it really is—so just see things as they are.