LYSANDER
Demetrius, I'll avouch it to his head,
Made love to Nedar's daughter, Helena,
And won her soul; and she, sweet lady, dotes,
Devoutly dotes, dotes in idolatry,
Upon this spotted and inconstant man. (1.1.108-112)
Hmm. This is interesting. Here, we learn that Demetrius was once engaged ("made love to") to another girl, Helena, before dropping her to be with Hermia. Long before the fairies' love juice causes Demetrius to fall back in love with Helena (2.2; 3.2), we learn that lovers can be fickle and erratic, even without the help of some magic potion.
Quote 2
LYSANDER
Ay me! for aught that I could ever read,
Could ever hear by tale or history,
The course of true love never did run smooth. (1.1.134-136)
This is one of the most famous lines of the play, and for good reason. Lysander's declaration pretty much sums up the play's notion that lovers always face difficult hurdles on the path to happiness—whether it's a disapproving parent, rival lover, or something else. In the play, Shakespeare makes this "love is an obstacle course" metaphor very literal when the young Athenians go chasing each other around the wood in pursuit of love. We're also interested in the way Lysander locates his love for Hermia in a long, rich "tradition." For Lysander, love is epic and the stuff of great literature and history.
Quote 3
LYSANDER
Or, if there were a sympathy in choice,
War, death, or sickness did lay siege to it,
Making it momentary as a sound,
Swift as a shadow, short as any dream,
Brief as the lightning in the collied night,
That, in a spleen, unfolds both heaven and earth,
And ere a man hath power to say "Behold!"
The jaws of darkness do devour it up.
So quick bright things come to confusion. (1.1.143-151)
Here, Lysander lists the obstacles that can separate lovers: "war, death, or sickness." Lysander also knows that, even though love can be explosive like "lightening," it's usually short-lived: "So quick bright things come to confusion."
P.S. The idea that love is transient, by the way, is a major theme in Romeo and Juliet, where Friar Laurence says the following about Romeo's passion: "These violent delights have violent ends" (2.6.1).