Things to remember
a. The rule of 20: This rule needs to be agreed by both partners. According to this rule, a hand is worth opening if the number of cards in the two longest suits + the sum of high card points is 20 or more, but ONLY if the points are in the two long suits. So, for example, if you have 10 points, and 5-5 (like West’s hand here) or 6-4 or 7-3 in two suits, and your points are in the long suits, the hand is worth opening! Same with 11 points and 5-4 or 6-3. According to this rule, a hand of 12 points with a 4-3-3-3 distribution is not worth opening 🙂 Yes, points are not everything. Distribution is very important and points in your long suits give power to the small cards in your long suit, and give a good chance for them to become potential tricks, especially (but not only) if one of these suits becomes trump (but long suits are useful in NT too).
b. To avoid the “danger hand”, you need sometimes to use special techniques, like loser on loser, or, like here, lose a Club trick on purpose, to keep West on the lead, so that later you can throw a Diamond loser and avoid losing the lead to East.
c. Developing a side suit via ruffs is an important tool to make extra tricks, when you hold a long side suit. Diamonds here has excellent potential for extra tricks. However, when established, you need to make sure you have an entry to that suit (via trump here).
d. It is very important to analyze the bidding. Counting that opponents have too little for what they promised (West promised 12 +, East showed 6-10… So how come they only have 16 points together?) – It should be clear that one of them has a distributional hand, in this case most likely the opener. So as he didn’t rebid Spades, he is likely to have long Clubs too. That means he is most likely to be short in Diamonds. From there you can infer that if You play ♦AK and a third Diamond, hoping to lose it to West… that probably won’t work.