The Missing Piece Meets the Big O, By Shel Silverstein.

The missing piece sat alone...
waiting for someone
to come along
and take it somewhere."

"Some fit...
but could not roll
Others could roll
but did not fit.
One didn't know a thing about fitting.
And another didn't know a thing about anything.
One was too delicate.
One put it on a pedestal...
and left it there.
Some had too many pieces missing.
Some had too many pieces, period.
It learned to hide from the hungry ones.
More came.
Some looked too closely.”

Others rolled right by without noticing.
It tried to make itself more attractive...
It didn't help.
It tried being flashy.
but that just frightened away the shy ones."

"At last one came along that fit just right.
But all of a sudden...
the missing piece began to grow!
And grow!
'I didn't know you were going to grow.'
'I didn't know it either,' said the missing piece.
'I'm lookin' for my missin' piece, one that won't increase....'
one came along who looked different.
'What do you want of me?' asked the missing piece.
'Nothing .'
'What do you need from me?'
'Nothing.'

'Who are you?' asked the missing piece.
'I am the Big O,' said the Big O.
'I think you are the one I have been waiting for,' said the missing piece. 'Maybe I am your missing piece.'
'But I am not missing a piece,' said the Big O.
'There is no place you would fit.'
'That is too bad,' said the missing piece.
'I was hoping that perhaps I could roll with you....'
'You cannot roll with me,' said the Big O,
'but perhaps you can roll by yourself.'
'By myself? A missing piece cannot roll by itself.'
'Have you ever tried?' asked the Big O.
'But I have sharp corners,' said the missing piece.
'I am not shaped for rolling.'
'Corners wear off,' said the Big O, 'and shapes change.
Anyhow, I must say good-bye..
Perhaps we will meet again....'
And away it rolled.
The missing piece was alone again."

"For a long time it just sat there.
Then... slowly... it lifted itself up on one end...and flopped over.
Then lift...pull...flop...
it began to move forward....
And soon its edges began to wear off...
liftpullflopliftpullflop...
and its shape began to change...
and then it was bumping instead of flopping...
and then it was bouncing instead of bumping...
and then it was rolling instead of bouncing....
And it didn't know where and it didn't care.
It was rolling!"