Canute really existed and really was king of England. The most told story about him, we don't know if it happened.

Canute took his courtiers down to the beach and ordered the tide to stop coming it. It didn't stop coming in, but kept on, as per eons old usual.

There are two interpretations of this story. One is that Canute was an arrogant idiot. Another is that Canute was teaching his aides the limits of his power.

Easy to imagine either--in the first, sycophancy has rotted his brain. In the second, the sycophants keep filling his ears with good ideas and bad ideas far beyond what the ruler to two seperate countries (he was also king of Norway) could possibly do in times of crummy transport and government that was decentralized to the point of barely existing above the village level, and he got tired of it, and told the good ideas folk to come on down to the beach.