One interesting point to note is that Arthurian legend, in its popular retelling, tends to show Arthur as "the chosen one", which is why he was able to pull out the sword.
The original stories tend to show that Arthur was worthy to become king because he understood he needed to apply the right amount of force, rather than trying to "overpower" it.
I don't think I would have understood the reference without having being told this recently; it is a trial that requires to be fully concentrated on sensing how the stone reacts to the moves.
I'm not sure which part of Arthurian legend your mentioning as original here, because Arthurian legends are... A rather deep well with no real canon as such. In the oldest versions, there is no sword in the stone, for example [0].
Along that line, Lancelot, who everyone knows, was a self-insert fanfic at one point. [1]
I don't think I would have understood the reference without having being told this recently; it is a trial that requires to be fully concentrated on sensing how the stone reacts to the moves.