In Much Ado About Nothing, Beatrice and Benedick are “tricked” into falling in love. How does it happen, and why is it so easy?
I would argue that the reason it is so easy is because they actually have very warm feelings for each other before the plot takes place. The game of wits between them is in fact a form of courtship. This is suggested later in the play when Benedick says, "We are too wise to woo peacefully."
Don Pedro and his friends plot to bring the couple together by making each of them believe the other is secretly infatuated with them. I think it is typical of human nature to warm to people we believe care for us. Additionally, it leads them to bring down their wits and be sincere with each other.
Once they start to treat each other kindly they become more convinced that what they have heard is true. This snowballs into what Don Pedro calls "a mountain of affection." The game of wits comes down and they can be honest about their affection.