Overoptimism

[op-tuh-miz-uh m] /ˈɒp təˌmɪz əm/

noun
1.
a disposition or tendency to look on the more favorable side of events or conditions and to expect the most favorable outcome.
2.
the belief that good ultimately predominates over evil in the world.
3.
the belief that goodness pervades reality.
4.
the doctrine that the existing world is the best of all possible worlds.
/ˌəʊvərˈɒptɪˌmɪzəm/
noun
1.
excessive hopefulness or confidence
/ˈɒptɪˌmɪzəm/
noun
1.
the tendency to expect the best and see the best in all things
2.
hopefulness; confidence
3.
the doctrine of the ultimate triumph of good over evil
4.
the philosophical doctrine that this is the best of all possible worlds
n.

1759 (in translations of Voltaire), from French optimisme (1737), from Modern Latin optimum, used by Gottfried Leibniz (in “Théodicée,” 1710) to mean “the greatest good,” from Latin optimus “the best” (see optimum). The doctrine holds that the actual world is the “best of all possible worlds,” in which the creator accomplishes the most good at the cost of the least evil.

En termes de l’art, il l’appelle la raison du meilleur ou plus savamment encore, et Theologiquement autant que Géométriquement, le systême de l’Optimum, ou l’Optimisme. [Mémoires de Trévoux, Feb. 1737]

Launched out of philosophical jargon and into currency by Voltaire’s satire on it in “Candide.” General sense of “belief that good ultimately will prevail in the world” first attested 1841 in Emerson; meaning “tendency to take a hopeful view of things” first recorded 1819 in Shelley.