Upon seeing the king the farmer said "Your Majesty, you should return to the palace at once because in just a short time I expect a huge amount of rain to fall in this area".
The king was polite and considerate, he replied "I hold the palace meteorologist in high regard. He is an extensively educated and experienced professional. And besides, I pay him very high wages. He gave me a very different forecast. I trust him and I will continue on my way".
So he continued on his way.
However, a short time later a torrential rain fell from the sky. The King and Queen were totally soaked and their entourage chuckled upon seeing them in such a shameful condition.
Furious, the king returned to the palace and gave the order to fire the professional.
Then he summoned the farmer and offered him the prestigious and high paying job of royal forecaster.
The farmer said "Your Majesty, I do not know anything about forecasting. I obtain my information from my donkey. If I see my donkey's ears drooping, it means with certainty that it will rain".
So the king hired the donkey.
Thus began the practice of hiring dumb asses to work for the government and paying them outrageous salaries to occupy its highest and most influential positions.
Spoiler:
the little scarlet pimpernel is a farmers weather glass it would nt need a wage 
