overoptimist

/ˌoʊvərˈɑptəmɪst/
noun
  1. A person who is excessively optimistic, often ignoring risks or negative possibilities.
    • The manager was an overoptimist and refused to create a backup plan.
    • Don't be an overoptimist; sometimes you need to prepare for the worst.
    • My brother is an overoptimist who always thinks he'll win the lottery even though he never buys a ticket.
Antonyms