I just consulted the blue jay in my backyard while watering the rose beds. He informs me that all rational birds know that lawn mowers do not exist, however belief in lawn mowers is socially useful because it gives otherwise shiftless birds a sense of morality and purpose in life. He encourages less enlightened birds to continue their belief in the lawn mower.
I told him to wait till next Saturday...
Xenophon's Cyropaedia (Books V-VIII)
24 minutes ago