By Upton Sinclair
It is difficult to get anybody to understand something, when their salary depends on them not understanding it.
— Upton Sinclair
Always keep financial incentives in mind.
I’ve updated this a little for the 20th century, because I think the idea applies equally to both men and women.
The original quote is:
It is difficult to get a man to understand something when his salary depends upon his not understanding it
This was first published in a book called I, Candidate for Governor, and How I Got Licked in 1934, around the time that Upton Sinclair was campagining to become Governor of California.
See: Quote Investigator
Never argue with somebody whose job depends on not being convinced.