Jade Holt pictures depression as a pack of hungry creatures, and the poem spends most of its length describing them: ink-black blood, scarred skin, dagger teeth snapping at nothing. The beasts live on misery, but the poem points out that other people's pain gives them little to eat, so they stay starved and furious. They hide from joy, which burns them, and come out only at night to attack the weak first, then batter the minds of the strong.
The speaker sounds both frightened and thoughtful. The short, blunt lines feel like a slow, creeping dread, and the dark imagery makes the mood heavy and claustrophobic. The final question changes everything. The "walls so carefully built" to hide sorrow might be keeping out the beasts, or they might be hiding pain from ourselves. That leaves the reader wondering whether the monsters are outside us at all, or whether they are something our own minds create.