Yeah, but a potato is hard before. An egg is soft, inside.

would that not be the very point of the aphorism, though? an egg may think boiling water is all that's needed without it accounting for the circumstances of the potato. and vice versa.

at least the potato doesn't stay up nights wondering which came first!

Just means we are all different and the same thing may have different effect. Still fully applies I think

That reminds me of the song lyric, “you can’t always get what you want; but if you try sometime, you’ll find you get what you need.” (Rolling Stones)

So ... Boiling water brings everything to the same hardness.

and rolled down