In A Midsummer Night's Dream, how does Puck's mistake complicate the relationships between the Athenian lovers?Act 2, scene 2
You have identified an important part of the plot that successfully complicates the situation and results in a hilarious farce of characters falling in and out of love with each other. Puck in this scene, having searched in vain for the "Athenian" that his master, Oberon, told him about, comes across a sleeping Lysander and Hermia. However, he misinterprets their separation (remember that Hermia insisted that they sleep apart because they were not married yet) as a dislike, and thus assumes that they are Helena and Demetrius:
Pretty soul, she durst not lie
Near this lack-love, this kill-courtesy.
Puck thus anoints the eyes of Lysander, who then unfortunately wakes up when Helena enters the grove, breaking into words of dramatic and exaggerated love:
And run through fire I will for thy sweet sake.
Of course, the irony is that Puck, in mistaking Lysander for Demetrius and calling him "lack-love" and "kill-courtesy" has actually accurately described Lysander's character in his swiftness to abandon his steadfast love for Hermia in favour of Helena. Thus the action of the play pokes fun at the propensity of humans to let ourselves be ruled by love, and also establishes how often these emotions are fickle and force us to act inhumanely.