We are excellent at deluding ourselves, a trait evolved for survival.
To survive difficult or desperate situations, we manipulate our state of mind: we create hope in the future to offset present misery.
On the other hand, clear-eyed assessment (i.e., grim realism) is pessimistic and/or cynical, disincentivizing survival by presenting a sober, truthful accounting that the odds are miserable. Our instinct, the survival imperative, encourages us to be irrational and to believe in our exceptionalism, which encourages perseverance against reality.