Although their pithy wisdom and seminal ideas expressed in this essay
aren't mine originally (arguably by now they belong in that public
domain known as folk lore), this presentation of them is mine
Fleas can jump extremely high - several times higher than a jar, in
If you put fleas in an open jar, they're fully capable of jumping right
out of the confinement of the jar.
Then if you put a lid on the jar ie if you close the jar, the fleas
jump and bump their heads on the lid. Pretty soon the fleas realize
they're not only unable to escape the confinement of the jar, but they
also realize they'll bump their heads on the lid if they jump as high
as they're fully capable of jumping.
So they learn to jump almost as high as the lid ... but
not quite as high. Fleas play it smart. They play it
safe. Fleas know their limitations.
They learn to jump only so high. They learn that jumping higher
than the closed lid is
They learn to jump not as high as they're capable of jumping. They
learn to jump only high enough so the don't bump their heads on the
But then if you remove the lid from the jar again ie if you re-open the
jar, the fleas still don't jump higher than the erstwhile
limit previously imposed on them by the closed lid - even though the
jar is now re-opened, even though they're fully capable of jumping high
enough to escape the confinement of the re-opened jar.
Piranhas, those South American fish (also known as Pirañas, and in
Venezuela as Caribes) with razor sharp teeth and a
voracious appetite for meat, don't fare much better. A similarly
pertinent story is also told about Piranhas
in an aquarium. It goes something like this:
It's feeding time. You introduce smaller less fortunate fish into the
aquarium. In seconds they're ripped to shreds, bloody targets of a
rapid Piranha feeding frenzy.
Then you put a clear glass divider exactly down the middle of the
aquarium, separating it into two areas with the Piranhas on one side of
the glass divider, and you introduce their lunch, the smaller less
fortunate fish, into the aquarium on the other side of the glass
A clear glass divider under water is completely transparent, so much so
that the Piranha don't even know it's there. In their frenzied attempts
to rip the smaller fish to shreds, they only succeed in bumping their
heads against the glass divider.
Pretty soon the Piranhas realize they're not only unable to reach their
lunch, but they also realize they'll bump their heads on the glass
divider if they
as powerfully as they're fully capable of
So they learn to
swimonly on their side of the aquarium. They learn to
swimalmost up to the glass divider ... but not bump into it.
Piranhas play it smart. They play it safe. Piranhas know
But then if you remove the glass divider from the aquarium, the
Piranhas still stay, hungry, on their side of the aquarium, the
side once limited by the glass divider, even though the aquarium is now
no longer divided, even though the Piranhas are fully capable of
anywhere they want to
even though they're fully capable of devouring anything they want to
The Piranhas also learned to set limits.
The Punch Line
Human beings have a lot in common with fleas as well as with Piranhas.