Mistakes I make in Bridge 1

This is the first posting in a new series "Mistakes I make in Bridge". For the record: The best contract in the hand above is 4♠, which make with an overtrick when played by North. After a heart lead to the K and the A, you can throw your ♦Q under the ♥K. This contract looks a bit academic, however. Even when South plays, it will make.

I spoiled my 3NT by refusing to think and make a plan. I do not know if that is a sign of aging or taking things too easy. The lead was a small diamond, which I gladly ducked hoping for an easy trick in diamonds. Lia likes to attack under Kings. But East won, and contrary to what most club players would do, opened the heart suit. It is now too late to establish the clubs.

There is one excuse for my play. Had I made this extra trick, I might make two overtricks if the clubs work. And it is rare that the opponents find the optimal defense.