For the purposes of this question, we neglect plays that don't matter (i.e. plays that don't affect how the hand plays out).

As I understand duplicate bridge, two teams play the same hand from different sides - so one pair plays E/W, the other plays N/S, for the exact same hand. The format is naturally balanced to wash out luck, and for one team to win the match, they need to win one hand by more than their team on the other table loses it by.

It also opens up the possibility for effectively the same contract and result to be repeated on both tables because all players involved agree that there is a "best play". How often does this happen?