Playing in a club game, you are in first seat and you pick up:
Do you open 1♥ or 2NT?
If you open 1♥ and it goes all pass you are in good shape. But you have a rebid problem if you open 1♥ and partner bids, either 1♠ or 1NT. Plus, you have three spades, so if partner transfers to spades over 2NT you will be happy. Therefore I think 2NT is the right opening bid.
So you open 2NT, LHO passes.
Then you have a problem.....
You pulled the 2♠ card out of the box instead of the 2NT card. Once LHO passes it is too late to do anything. It is very important not to say anything or flinch after that, as partner must not have that information. You also must not give the opponents any clue, maybe they will balance.
But partner didn't take a call and neither did the opponents so now you have to play 2♠.
The lead is the ♦Q....
Plan the play.
Clearly, you will never get any more than two diamond tricks. On this lead, you may only get one. Therefore you should win the ♦K in dummy and take the club finesse. You can use a heart ruff to take a second finesse if it wins.
Your plan should be to win two diamonds, two or three clubs, the ♥A, ♠A, two heart ruffs, and a diamond ruff with the ♠Q. If all goes well you might get nine tricks.
So you win the ♦K and play a club to the ♣Q. It loses to the ♣K and back comes a diamond. RHO ruffs that and plays the ♣T which you win with the ace. Now what?
It's time to crossruff.
Play ace and ruff a heart. Then you will have to decide how to get back to your hand. If you try to ruff a diamond to hand, RHO might discard a club and ruff the ♣J. But, that would put him with a singleton diamond and doubleton club, which is not as likely as RHO having three clubs.
After the ♥A and a heart ruff, you decide to play a diamond from hand. RHO ruffs in with the ♠J and you overruff with the ♠Q. Next you try to cash the ♣J but LHO ruffs. He plays the ♠K and RHO plays the ♠9. As your last chance you try to ruff a diamond in your hand with your last trump and it lives. East only had three trumps. So you make 2♠.
Here's the full hand.
On a 17 top, +110 was worth 5.5, which is 32% of the matchpoints. Why?
The normal lead against 3NT is a spade to the five, jack, and queen. Some players decided to play for diamonds 3-2 by playing ♦A and ♦K. Now you can't recover. Four pairs went down in 3NT. One pair went down in 5♦. The half matchpoint came from someone in 3♣ making 3.
It's best not to make mechanical errors like this. I had misplayed the previous hand and I was still thinking about it when I pulled the wrong card out of the box. Don't do that! Put the previous hand out of your mind, it is over!
But if something like this happens to you, do not lose focus, do the best you can. You might be able to salvage some matchpoints.
Plus... it's free!