Indispensable advice

Sometime when you’re feeling IMPORTANT
Sometime when your ego’s in bloom.
Sometime when you take it for granted
You’re the best qualified one in the room.
Sometime when you feel that you’re going
Would leave an unfillable hole.
Just follow this simple instruction
And see how it humbles your sole.

Take a bucket and fill it with water
Put your hand in it up to the wrist,
Pull it out and the hole that’s remaining
Is a measure of how you’ll be missed.

The moral of this quaint example
(as quoted by poets anon.)
Be proud of yourself but remember
There is NO INDISPENSABLE ONE.