Soso literally translates to 'bland' or 'tasteless'. While you can use it to describe unseasoned food, it's also a perfect word to call a person or situation 'dull'.
In the lyrics, the singer feels he was once "el más soso grano de sal" (the blandest grain of salt)—a powerful metaphor for feeling insignificant and without purpose. Learning this word unlocks the core emotional contrast of the song, where love transforms him into part of "la torre más alta de la ciudad" (the tallest tower in the city).
Spanish singer-songwriter Iñigo Quintero leans right into his own insecurities here, and the result feels surprisingly genuine. He kicks things off by admitting he can be difficult to deal with: "Sé que estoy algo insoportable" ("I know I am a bit unbearable"). Instead of pretending to be smooth, he views himself as tiny, overlooked, and frankly a little boring. He literally stacks up self-deprecating metaphors, calling himself "la última gota del mar" ("the last drop in the sea"), "una simple miga de pan" ("a simple breadcrumb"), and "el más soso grano de sal" ("the blandest grain of salt"). In Spanish, soso is a great word for anything dull or lacking flavor, so admitting you are a tasteless grain of salt is peak honesty.
Yet, being with this person completely flips his world upside down. He keeps repeating the question "¿Cómo lo haces?" ("How do you do it?") because together they have transformed from insignificant specks into "la torre más alta de la ciudad" ("the tallest tower in the city"). He talks about missing the simple days when they could "vivir descalzo" ("live barefoot"), admitting that the distance hurts because "odio siempre que nos separamos" ("I always hate it when we separate"). It turns out feeling like an invisible crumb does not matter at all once someone makes you feel towering over the whole skyline.