The "par" result on a deal occurs if both sides bid and play perfectly. Because bridge is played by imperfect creatures, "par" is often achieved when both sides make errors that cancel each other.
In today's deal, North's first two bids showed some diamonds and about 11 points. (North did not promise balanced pattern, though he would often have it.) When South rebid three spades to sign off, North should have passed. Instead, he looked at his three top tricks and broke discipline by raising to game.
West led a heart, and South was faced with four losers: two hearts, a club, and at least one trump. East took the K-A and led a third heart, and South ruffed and cashed the A-K of trumps. When East-West followed, declarer shrugged and conceded down one.
Clearly, North-South failed to meet par in the auction. Did either side come up short in the play?
After the first three tricks, South's game was cold. He could cash the A-K of trumps and next go to the ace of diamonds and ruff dummy's last heart. South could then take the king of diamonds, ruff a diamond, and cash the K-A of clubs. Having won nine tricks, he could lead dummy's last diamond and ruff it, as West had to follow.
Could the defense do anything about that? When East led a third heart, he helped South score his low trumps. If instead East shifts to a diamond at Trick Three, he upsets the timing for any winning play, and South goes down.