Derrumbar means to knock down, demolish, or collapse. The past participle derrumbado (collapsed/crumbled) is used here to describe a state of being completely broken or fallen apart.
In the song, Diego Torres sings, "En un segundo te puedes derrumbar" (In a second you can collapse). This powerful verb captures the sudden and dramatic way life can change, emphasizing vulnerability and the unexpected challenges we face. It's a vivid and impactful word that goes beyond simple sadness to convey a complete breakdown.
Diego Torres built "En Un Segundo" around a single admission: he can't tell which side of anything he's actually on. He opens plain — "La vida viene y va" (Life comes and goes), "Entre el bien y el mal" (Between good and evil) — and a verse later says it outright: "Quisiera saber de qué lado está Dios" (I'd like to know which side God is on), "Y de qué lado estoy yo" (And which side I'm on). The chorus never settles that; it just times how fast the ground can move underneath it — "En un segundo, todo cambiar" (In a second, everything can change), "Y todo puede ser tan simple y tan complejo" (And everything can be so simple and so complex).