One example of the theme, "The course of love never did run smooth," can be seen in Oberon and Titania's relationship. Oberon's jealousy of Titania's beautiful foundling Indian boy is especially interesting. Literary Shirley Nelson Garner points out that Oberon's jealousy seems to stem from both a physical attraction for the boy, but also the desire to have Titania's affection all to himself. We know that Oberon is physically attracted to the boy as Puck describes the boy as a "lovely boy" and says that Titania "never had so sweet a changeling" and even describes Oberon as "jealous" (II.i.22-24). We also know that Titania feels a deep physical attraction because Puck states that she "[c]rowns him with flowers, and makes him all her joy," which happens to be the exact same way she treats Bottom after falling in love with him as a donkey (II.i.27). Garner further points out that the reason why Titania is caring for the boy is significant. She is caring for him because, as she states, "His mother was a votaress of my order," meaning that his mother was a "devout worshiper" of Titania. In fact, Titania continues to describe a very close bond between herself and the child's mother. Apparently this bond was enough to make Oberon jealous. In wanting to take the child from her, he not only wants what he finds physically attractive for himself, he wants to sever a bond that has prevented Titania from bestowing Oberon with her full affection. Now that the child's mother has died, Titania is bestowing all of her affection on the child and not bestowing any affection on Oberon. Hence, Oberon is jealous of the boy for two reasons: 1) He finds the boy physically attractive; and 2) He wants Titania's affection all to himself.
Oberon's jealousy leads to an ongoing quarrel between the two, showing us that love is not a smooth course to travel. Their longstanding quarrel is becoming so troublesome that the seasons have actually become mixed up, as we see in Titania's lines:
The spring, the summer,
The childing autumn, angry winter, change
Their wonted liveries; and the mazed world
... knows not which is which. (112-115)
Hence, we see through Oberon and Titania's relationship that the course of love is not a smooth one.
Other examples can be seen in the Athenian couples' relationships. Helena struggled greatly to obtain Demetrius and Hermia struggled just as much to win Lysander back.