Comment by EdwardCoffin

Though I was confident this was just a metaphor, I did try cracking a walnut using this method. I submerged three walnuts in a jar with some tap water, and let them sit for three years before trying to open them.

It was a let-down: they were easier to open, but certainly not by hand, I still had to use a nutcracker. They smelled bad, too. I did not try eating them.