Nemo dat quod non habet
“No-one can give what he does not have.”
“You can only give as good as you get”
A Latin maxim of relevance to assignees and purchasers for value, which was roundly ignored by whoever the bright spark was who came up with the preposterous idea of rehypothecation.
It is also useful in deflating drafting pretensions of people who come bearing gifts like “nor anyone acting on its behalf”.