Good players sometimes err

We were playing in a club game against the best pair in the room (they'd go on to win, with a 69% game). We are North-South (I am South) and we get too high in the auction:

.

Board: 16

Vul: N-S

Dlr: North

N

North

♠

10x

♥

Qxx

♦

xxx

♣

QJ10xx

.

W

Defender

♠

Kx

♥

xxx

♦

Qxxx

♣

Axxx

Lead: ♦4

E

East

♠

Qxx

♥

xxx

♦

Kxxx

♣

xxx

.

S

Me

♠

AJ9xxx

♥

AKJx

♦

Ax

♣

K

.

The bidding goes:

W

West

N

North

E

East

S

Me

—

Pass

Pass

1♣¹

Pass

1♦²

Pass

2♠³

Pass

3♣

Pass

3♥

Pass

3NT

Pass

4♠

All Pass

(1) 16+ artificial

(2) 0-7, artificial

(3) 20+, 5+ spades

I get the lead of a low diamond and immediately, I see that I have one loser each in clubs and diamonds. I need to play the spades for one loser, but there is only entry in dummy, so I can not take two spade finesses.  Any ideas?

I took East's King of diamonds with the Ace and decided to see if I could sneak a trick past them. I led the king of clubs like a man who has Kx and wants to enter dummy to take a finesse.  West took his Ace of clubs though and cashed his Queen of diamonds.  He then played a third diamond and I ruffed.  What now?

I went to dummy with the Queen of hearts and tried to run the 10, but West had the King of spades. He now thought for a while and put a club on the board.

Time for thought.  From the bidding (2S-3H-4S), everyone at the table knows that I have 6 spades and 4 hearts. I have already shown up with 2 diamonds and therefore, I could have had only the singleton king of clubs. Why would West put me on the board, begging me to finesse the spade again?

Only if he had the KQ tight of spades! In that case, he'd be worried that if I was stuck in my hand, I'd have no choice but to bang down the Ace, felling the queen and making the contract!

So, I led spade from dummy. East played a low spade. Decision time.  I decided to go with my gut. West could not have made such a rookie mistake as to give me a finesse opportunity if the finesse was working. I went up with the Ace.

Wouldn't you know it?  East had the Queen of spades.  They had given me the opportunity to make the contract by making a defensive error and I didn't believe that they had ...