If East had held the heart ten or king, he would have played that card, not the jack.

So there was, apparently, reason to think that East held the queen.

West played low, which would perhaps have been right if East had held the king.

He was sure that East held all four missing hearts.

There was a fair chance that if East held the king, he would either cover the jack or think about doing so.

Consider what would have happened if East had held the club ten instead of the heart queen.

He was down one, and astonished to find that East held the heart king.

It would not have been if East had held more than three diamonds.

It also increased the chance that East held the diamond king.

But that would have been wrong if East held the nine.