Unferth questions Beowulf's abilities. What battle does he say Beowulf lost?

At the feast, a Dane named Unferth, envious of his kinsmen's admiration of Beowulf, begins to taunt the Geat. He claims that Beowulf once lost a swimming match against Breca and that Beowulf will meet with defeat for a second time when he faces Grendel in the mead-hall.

teenagers are certainly stereotyped as moody.

most people view teenagers as naturally moody and grumpy, even when this is wrong. many teens are suffering from depression but it is brushed off as "just a phase" or "that's just cause they're a teenager"

the answer a: perseverance !