Can a man of full age and understanding sign a legal document?

Lord Denning, M.R., in Gallie v. Lee and another, [1969] 2 Ch. 17 at pages 36 to 37, states: Whenever a man of full age and understanding, who can read and write, signs a legal document which is put before him for signature - by which I mean a document which, it is apparent on the face of it, is intended to have legal consequences - then, if he does not take the trouble to read it but signs it as it is, relying on the word of another as to its character or contents or effect, he cannot be heard to say that it is not his document. By his conduct in signing it he has represented, to all those into whose hands it may come, that it is his document.