Cabeciduro is a colloquial and expressive term that literally means "hard-headed." It's a less common word than its synonyms, making it stand out.
In the song, Arcángel uses it to describe himself, saying, "Por pendejo, por cabeciduro" (For being an idiot, for being hard-headed). This reveals his self-reflection on past mistakes and stubbornness, adding a layer of personal vulnerability to the lyrics.
Arcángel's "Mi Peor Momento" is a really honest look at dealing with tough times, even when you're trying to keep it together on the outside. He talks about smiling all the time even when he's "muerto por dentro" [dead inside], and giving his best even in his "peor momento" [worst moment]. It's a relatable feeling of putting on a brave face when you're struggling internally.
He opens up about feeling lost and disconnected, even saying "a veces no me siento vivo" [sometimes I don't feel alive] despite his heart beating. He mentions how hard it is to express himself, only really finding the words when he writes. Arcángel also touches on the profound grief of losing his brother, Justin, feeling like it was a punishment, and how that loss made him question everything. But ultimately, it's a song about finding strength even when you're at your lowest, learning that "los diamantes se hacen bajo presión" [diamonds are made under pressure], and realizing that life's struggles are a "tormenta divina que vale la pena pasar" [divine storm worth going through].