Ingannare means "to deceive" or "to trick." It's a strong verb that implies a betrayal of trust, making it more impactful than simpler words for misleading someone.
In the song, the line "Non mi puoi ingannare mai" (You can never deceive me) highlights a deep sense of trust and understanding between the lovers. It suggests that their connection is so profound that deception is impossible, adding a layer of intensity to their relationship.
Grignani opens with a promise stated plainly, twice, like a vow: "Io son sempre stato tuo" (I have always been yours) answered by "Tu sei sempre stata mia" (You have always been mine). There's no build-up to it, no metaphor to unpack first. He just says it, and the song spends the next few minutes proving he means it.
The doubt shows up in the bridge, and it's an odd kind of doubt. He admits "Io io che da lei scappavo" (I was the one who ran away from her), then flips the accusation back on himself with "Perché mi puoi tradire" (Because you can betray me) and "Non mi puoi ingannare mai" (You can never fool me). He's the one with a past, yet he's the one setting the terms of trust. Later he calls love "una sfida" a challenge, only to take that back too: "Che amarsi no non è mai una sfida, ma è come cercare in noi una guida" (That loving each other is never a challenge, but it's like looking for guidance within ourselves). That's the whole argument of the song in two lines - love isn't a fight to win, it's a compass you check together.