Diario degli errori literally translates to "diary of mistakes". It's a striking and evocative phrase that immediately sparks curiosity.
In the song, Michele Bravi uses this phrase to represent a collection of his past missteps, regrets, and imperfections. He asks someone to remain outside of this "diary," implying a desire to protect them from his flaws and past troubles, making it a deeply personal and poignant expression.
Michele Bravi brought this song to Sanremo in 2017, and it reads like a confession written in a notebook. The singer lists what he has got wrong: he went "sempre dritto come un treno" (always straight ahead like a train), he never said "resta" (stay) when he could say "addio" (goodbye), and he "ho sempre avuto troppa fretta" (always was in too much of a hurry).
The chorus turns all of that into a request to one person: "Almeno tu rimani fuori / dal mio diario degli errori" (At least you, stay out / of my diary of mistakes). He doesn't ask to be forgiven. He asks that this one relationship stay clean of his habits. The second verse gets darker, with "Ho giocato con il fuoco" (I played with fire), a common idiom in Italian just like in English, and "un mattino senza alba" (a morning with no dawn).
Listen for "almeno" (at least): it opens nearly every chorus line, and it carries the whole song's humility.