The best advice is to concentrate
Frank Stewart has written several books and a lot of newspaper columns. One of the former is “Keys to Winning Bridge” (Baron Barclay Bridge Supplies). It is subtitled “The Advancing Player’s Handbook for Success.”
Stewart covers all three sectors of the game, in order: declarerplay, defense and bidding. The book ends with two short chapters on winning attitudes and maintaining focus. The prologue states: “The level of instruction varies. Some ... is elementary ... some ... more advanced ... Although my aim is to build a sound foundation, I also want to give any reader who can excel the opportunity to do so.”
This deal is instructive. South was in two no-trump. West led the spade three: two, 10, king. Declarer played a diamond to the ace and returned to a diamond to his jack. West took that with his queen and found the excellent continuation of the spade nine. When that held the trick, West led his spade seven to his partner’s queen. Now, though, East shifted to a heart, not to a club, so the contract made instead of going down one. Who was to blame?
North had to go via Stayman to invite game because an immediate two-no-trump response would have been a transfer to diamonds.
At first glance, it seems that East erred, but as Stewart points out (he was East), West was so happy with his spade-nine play that he stopped thinking. At trick five, West should have cashed the club king, king from ace-king after trick one. Then East could not have gone wrong.