There is another theory that the last character '玉' of the word 被褐懐玉 (lit. Clothes do not make the man. Fine clothes make not a gentleman.) described in "Te Ching" (the last volume of Lao-tzu's "Tao Te Ching ") was replaced with '石'.
また老子の『徳経』（『老子道徳経』　下篇）にある被褐懐玉の玉を石に置き換えたとする説などである。