I think about the words to this poem:
Sometime, when you're feeling important, sometime, when your egos in bloom.
Sometime when you feel without question you're the best qualified in the room.
Sometime when you feel that your going would leave an unfillable hole
just follow this simple instructions and see if they humble your soul.
Take a bucket and fill it with water, put your hand in it, up to the wrist,
take it out, and the hole that's remaining is the measure of how you've been missed.
You can splash all you like as you enter, you can stir up the water galore.
But stop .. and you'll find in an instant it will look just the same as before.
The moral of this quaint example is to do just the best that you can
and be proud of yourself, but remember ..
There is no indispensible man !