The speaker in "The Wanderer" is completely miserable because he has lost his loved ones and his lord (the local ruler that he was loyal to), and must now wander over the ocean far from home. This situation means that, to add insult to injury, he doesn't have anyone with whom he can share his sorrows. He's not convinced, however, that speaking about sadness is a good idea, and he often suggests that a wise man will keep his thoughts locked away in his mind or heart. He describes sadness as a wound to his heart. It's a wound that can never heal, since every time he remembers what he has lost the wound reopens.
The speaker of "The Wanderer" can never escape his sadness because of the happy memories that haunt him.
"The Wanderer" argues against its own existence by telling the readers that a wise man should lock sad thoughts away in his heart, never to speak of them.