In scientific forecasting the most favourable outcomes that can be projected are bounded by the limits of extrapolated data. An optimistic expectation based on nothing but its desirability obstructs further information gathering and reasoning; inhibits directive or corrective actions; and invites disaster.
A characteristic feature of the period of economic summits is that, whatever the state of the world economy, the leaders of the principal industrialized countries will profess themselves largely content with the situation and prospects.
It is impossible for an optimist to be pleasantly surprised.
Despair is the deadliest of all sins, but compared to hope you at least know where you are.