(Greek, thura; Anglo-Saxon, dora.)
The door must be either shut or open. It must be one way or the other. This is from a French comedy called Le Grondeur, where the master scolds his servant for leaving the door open. The servant says that he was scolded the last time for shutting it, and adds: “Do you wish it shut?”—“No.”—“Do you wish it open?”—“No.”—“Why,” says the man, “it must be either shut or open.” He laid the charge at my door. He accused me of doing it. Next door to it. As, if not so, it was next door to it, i.e. very like it, next-door neighbour to it. Sin lieth at the door (Gen. iv. 7). The blame of sin lies at the door of the wrong-doer, and he must take the consequences.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894