Hugh Kelsey, the bridge writer, in one of his books on Improving Your Partner's Play wrote of an important technique, which is almost an everyday occurrence defending 3NT. The attached example where the mentor sat West and the protege sat East is a case in point.
The ending on the left arose with myself, the expert on lead. I momentarily forgot Kelsey's advice and needlessly put partner to a test or a memory squeeze by cashing my second good spade on trick twelve. Instead, knowing that partner had a club and diamond winner I should exit one trick earlier when partner has two winners left and does not choose the wrong one to throw away. Remember this advice, it will save many disasters in individuals, lower flight games, and in new partnerships.