Mort Drucker didn't like the way he drew this knob, so he painted it out and re-drew it.
The knob was located on the back of an electric lamp:
Over a chaotic surgical table:
In a crowded operating room:
Surrounded by even more bystanders-- from a vampire to a clergyman-- in a splash panel for MAD Magazine:
MAD reproduced Drucker's drawing small enough so that it's doubtful a single reader saw that damn knob. Yet, Drucker painted it out and did it all over again.
Charles Dickens wrote to his son,
I should never have made my success in life if I had been shy of taking pains, or if I had not bestowed upon the least thing I have ever undertaken exactly the same attention and care that I have bestowed upon the greatest.