This is the one I have thought hardest about, because it is counter-intuitive and because it is, I now think, the actual technique.

Christian Dupont was, in three years, scrupulously honest about trivia.

He told me when he was in a bad mood and why.

He told me he had had two drinks when he had had two drinks.

When he forgot something he said he had forgotten it instead of inventing a reason.

Which means that in three years I never once caught him in a small lie, and a person who has never caught you in a small lie does not go looking for a large one.