Couplet Summary

Line 13

For sweetest things turn sourest by their deeds;

• So what's the speaker talking about here? Is he still talking about the flower from lines 9-12, or has he reverted back to talking about humans?
• Given that flowers aren't usually known for their great "deeds," we're going to go with humans on this one.
• Note the word "For" at the beginning of this line; this is a clue that Shakespeare thinks of it as offering an explanation for what has come before. It's like he's saying, "because" or "as" instead.
• Basically, he's saying that the "sweetest things"—that is, the best people—"turn sourest by their deeds"—that is, their deeds turn them into the worst people.
• From the context, we can assume that this is because their "deeds" are bad. And you are what you do—or so they say.
• When you have very high expectations of someone to begin with—and we'd say that calling a group of people the "sweetest things" sounds like pretty much the highest expectations—the chances are high that they'll disappoint eventually. And, when they do, they can seem like they turned into the worst people overnight. 
• If any of this sounds at all familiar (and Shmoop bets it does), you should have a clear idea about what Shakespeare is talking about here. Now we can see why he was so impressed by the people who have "pow'r to hurt and will do none." By not doing bad "deeds," the powerful people can remain in the speaker's good books. They don't turn sour.
• But if they do succumb to temptation and hurt other folks, well, then they're just the worst. The living worst.

Line 14

Lilies that fester smell far worse than weeds. 

• It looks like lines 13 and 14 are a one-two punch. Line 14 really goes for the gut, doesn't it?
• Shakespeare's spot on here, too. Lilies that have rotted really do smell terrible, and they smell way worse than any weeds we've ever smelled.
• In any case, it isn't hard to see how this line matches up to the ideas in line 13, just as the flower imagery in Lines 9-12 matches up with the human imagery in lines 1-8. As you've probably figured out, the "Lilies" are like the "sweetest things," which, as we know, are really powerful people. Just as the "sweetest things" become the "sourest" when they behave badly, so do "Lilies" turn out to smell worse than "weeds" once they rot. 
• So what's this mean for the poem as a whole? Well it goes back to those powerful people way back in line one. If those people who have the power to hurt hold themselves back and manage not to hurt others—in other words, if they show restraint—well then they'll stay lilies. 
• But if they do hurt people, they're even worse than weeds—they're rotten, stinky, and generally awful. So a great and mighty person who does something bad is way, way worse than a person who wasn't all that great to begin with. Ah, Shakespeare. Lesson learned, buddy.