West North East South Pass Pass Pass 1 Pass 4 * All Pass *Practical rather than Scientific Opening Lead: CK, C2 to East’s CA, H4 returned by East. Do you play HK or HJ at trick three? Recommended Line: Everybody hates guessing when holding a K-J combination – exactly the problem you face at trick three in this hand. Some will toss a coin, metaphorically or literally.
A few will keep their coin in their pocket, and use careful analysis. Here is your chain of logic.
West holds five points in diamonds (two of which are assumed, reasonably enough). You need the diamond finesse to succeed, so you “give” West the K. That adds up to eight points. If West also held the A, he would probably have opened. So, to be consistent with your allocation of the K to West, assume East holds the A, and play the K. Think like that, and you’ll be coining it in the long run.