It pays to have a full quiver of competitive tools. East's responsive double provides a way for East to suggest values and pattern.

4♣ would be impregnable but not easy, while 4♦ is beatable, but not easily. Will North, against 4♦, lead partner's suit, the ♥A? If so, the contract can no longer be defeated legitimately. West will place the ♦KQ in the South hand for the opening bid, and North has squandered his entry to give South the needed club ruff.

Leading unsupported aces is not often best, or necessary, even in partner's suit, and I am happy to be able to point out another time it is wrong. It takes a black suit lead to defeat the contract.

In a club contract, declarer has entry problems, so must take an early position in diamonds by leading to the ♣Q and playing a SMALL diamond (not the ♦T), intending to play the jack on a small card by South. When South splits, trumps may be drawn and a diamond to the carefully retained ♦T will promote the diamond suit. Had the ♦T been led, there would be no entry back to dummy to lead diamonds again toward the jack, and the contract would be set.