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;
But either it was different in blood—
O cross! too high to be enthrall'd to low.
Or else misgraffèd in respect of years—
O spite! too old to be engag'd to young.
Or else it stood upon the choice of friends—
Hermia:Midsummer Night's Dream Act 1, scene 1, 132–140
O hell! to choose love by another's eyes.
The young lovers Lysander and Hermia, like young lovers in every comedy, have run into trouble at the very start of the play. Hermia's father has decided that she shall marry Demetrius, not Lysander; if she refuses, she'll have to face the law of Athens—that is, either death or consignment to a nunnery. Lysander offers "comfort" with the observation that "the course of true love never did run smooth," apparently comparing romance to a river current. His examples—which elicit parallel replies from Hermia—include affairs complicated by differences in class ("blood") or age, or dictated by relations ("friends"). I haven't quoted the rest of his complaint, expecting that this sample should be enough. (For the rest of the catalogue, see SWIFT AS A SHADOW.) Hermia's "misgraffèd," by the way, means "poorly grafted"; she compares marital union to hybridization. Horticultural metaphors are common in Shakespeare [see GET THEE TO A NUNNERY].