Just finished subbing for 6 boards in a matchpoints tournament.  Three of the 6 boards were total disasters.  Here's the first board I played:

All red, 2nd:

AQ652 / JT8 / JT / AT2

 

Righty opens 1 Diamond.  I bid 1 Spade.  Pard bids 1NT.

That gets passed around to Lefty, who bids 2 Diamonds.  Now pard's in for 2 Hearts.

Righty now bids 3 Diamonds.

And now?

I certainly expected partner to make 2 Hearts, so I have to protect the plus, no?  I smashed it.

Now I get to figure out what to lead.

A Heart and a trump seem to be the 2 obvious contenders, no?

I chose a trump (they don't seem to have many tricks outside of Diamonds and pard did bid 1NT.)

J7 / 742 / 76432 / K93 Dummy (LHO)

AQ652 / JT8 / JT / AT2 You

Huh?  That's a lot of Diamonds in dummy.

Declarer won the Ace (good news, I guess, at least I didn't pick off pard's Kx) and led a Spade (the 8) up.

Do you duck or win?  If you win, what do you play next (pard follows with the 4 if you win)?

...

I won and played the Jack of Hearts.  I was hoping to get partner on lead so that he could clarify the Spade situation for me (I know he has a doubleton, but is it Kx?)

Declarer won the Ace, cashed the King of Diamonds (dropping partner's Queen) and played the 9 of Spades up.

Now what?

Well, now your only chance is to duck and hope that partner had Kx.  Assuming partner has 5 Hearts the most we can score is 2 Spades, 1 Heart and 1 Club from here (the other 2 Clubs can be pitched on Declarer's Spade spots) if we play the Ace of Spades now.  (Our only OTHER hope would be to win the Spade and underlead the Club, hoping for a misguess and risking an uptrick if Declarer gets it right.)

The Jack of Spades won the trick (partner started with 43) and Declarer eventually scored up +870.

The only lead to beat the hand legitimately was a round suit.  - Strike 1

When Declarer slipped by not drawing trump immediately, giving partner a Spade ruff still lets the defense score 2 Spades, 1 ruff, 1 Heart and 1 Club.  That's where I made my UGLY mistake.  I know partner can overruff dummy; playing him for either the Ace or KQ of Hearts seems like the percentage decision.  Starting with the 8 from T983 is a good normal falsecard, so I don't think that helped me much. - Strike 2

Letting the uptrick through was one of those ? situations.  When Declarer continues with the 9, he's almost 100% to have started with KT98 (Why would he waste the 9 if he still had the 3?) but it seemed like the only hope (and to be honest, I didn't look QUITE that deeply at the table.)

-870 (or even -670) was worth 0% of the matchpoints (in a 34 table game that's no mean feat.)  +200 would have been worth 94% of the matchpoints.

J7 / 742 / 76432 / K93

KT98 / A3 / AK98 / 864