a man who is his own lawyer has a fool for a client

a man who is his own lawyer has a fool for a client

A man who tries to defend himself, rather than hiring a trained lawyer, is a fool. A: "What do you mean, a lawyer? I'm going to represent myself!" B: "Well, just keep in mind that a man who is his own lawyer has a fool for a client."
See also: fool, lawyer, man, who