This hand doesn't show our system to best advantage. Jon was maximum for his 1NT response, so he jumped to 3 in case we had enough for game. We didn't have enough for game, but we didn't have enough diamonds for 3 either, so I tried 3, and chose to remove 3NT; perhaps it's better to take my chances there. By the end of the auction I had systemically shown four spades, three hearts, five clubs, and one other card which ought systemically to be in a spade or diamond (unlikely to be a diamond as a matter of bridge logic).
Against 4, East sensibly led a trump, which went to the nine and king. I tried a spade to the four, queen and ace. West, who knew a lot about the hand, now went subtly wrong by switching to a diamond - a simple trump continuation is good. I discarded a club from hand, and won with South's ace. The best play now is to ruff a diamond, cash the queen of hearts, and lead the ten of spades, choosing between running it and trying to ruff down the jack of spades, in both cases needing the diamonds blocked.
However, I went wrong myself by leading the jack of clubs from dummy at trick four, giving West another chance to beat the contract by putting in the queen, leaving me in the wrong hand to take the diamond ruff I needed to block the suit. Instead he took the ace and forced my hand with a diamond, getting me back on the winning line. I needed to guess the spades, and got it right, thinking that East might well not have petered with jack to four - I was lucky about this too, while I was dithering about it, I cashed the king of spades, and only then noticed that the ruffing finesse would no longer help.