This apocryphal story about Canute is often misunderstood.
Canute did not think he could command the tides. But some of the fawning sycophants in his Court claimed that he was "God" (probably for their own personal gain). Canute got fed up with all these people thinking they would profit by "blowing smoke up my arse".
In order to prove the point (that he was definitely not "God"), Canute had his throne moved to the low tide mark, and publicly commanded the sea to not advance. Of course, the tide came in (which was witnessed by the entire Court), and Canute had to be removed to higher ground.
It was then obvious to everyone that Canute was not omnipotent; therefore he was not "God", and the ridiculous claims stopped.
I think Canute was actually a fairly reasonable King, as far as Kings of those times go.
Somehow, over time, the meaning of the story got switched around.
