The Cage Bird and the Bat_英语寓言故事

a singing bird was confined in a cage which hung outside a window,
and had a way of singing at night when all other birds were asleep.
one night a bat came and clung to the bars of the cage, and asked
the bird why she was silent by day and sang only at night. "i have a
very good reason for doing so," said the bird. "it was once when i was
singing in the daytime that a fowler was attracted by my voice, and
set his nets for me and caught me. since then i have never sung except
by night." but the bat replied, "it is no use your doing that now when
you are a prisoner: if only you had done so before you were caught,
you might still have been free."

"precautions are useless after the crisis."