Initiation

Key Plays at Notrump I'm having trouble understanding the first deal in the page. Here's what I have so far: If we assume that the only way to make the contract is to establish clubs, i.e., we assume that the opponents have a distribution of 3-2, then the only problem is the opponents taking 2 tricks in either spades or hearts. WLOG assume that they have a 5-3 distribution in hearts; this means that there is one dangerous opponent. 1) If we duck clubs first hearts will be unblocked after playing the first diamond, therefore ducking loses if the dangerous opponent has a Kx or Ax in diamonds (with probability > 50%). 2) If we instead play diamonds first, hearts will become unblocked after playing both diamond losers so the dangerous opponent can gain the lead if (s)he has a third club, which based on our assumption of a 3-2 club break (that the contract is makeable), has probability less than 50%, since (s)he already has more hearts than his/her partner. Therefore diamonds first are correct. Based on the other deals though I think there is something more concrete and simple that I am missing. Do you know what it is?