Lawyers tell their clients this right before they, the client, is deposed. As another commentor here hinted at, when being deposed you are either going to play it safe or lose, there is really no winning. Deposition hiccups are later used, at trial or in settlement negotiations, as leverage against your opponent or to try to discredit them as a witness/simply make them look stupid as a witness. A deponent seldom has anything to gain from waxing poetic about whatever they are being deposed about.

That's the litigation game.

Edit: spelling.