No man can flay a stone.

The saying states that effort cannot obtain something a thing does not possess. A stone has no skin to remove, so the proposed task is impossible from the outset rather than merely difficult. Here “man” reflects older generic wording.

It can reject unreasonable demands or expectations, especially when someone is asked to supply value, resources, or results that are simply unavailable. The emphasis falls on the limits of the situation, not on a lack of willingness or skill.

Use it when explaining that no pressure or ingenuity can draw a requested benefit from a source that has none to give. Its imagery is stark and figurative; “man” is an older generic term, so a gender-inclusive paraphrase may suit modern contexts.