Fleas

Fleas put in a jar will jump out.

Fleas in a jar with a glass plate across the top will jump,
hit the plate, and stay in the jar.

Eventually, fleas in a jar with a glass plate across the top
won’t jump high enough to hit the plate.

If the fleas stop hitting the plate,
and the plate is removed,
the fleas won’t jump out.

If the removed glass plate is a metaphor for fear,
are you certain you’ve not been conditioned to fear glass plates
that aren’t there?