A regret is something where you look backward at something that where you had control, where you had some agency Where you had some agency, you did something that, well, you did something wrong, and it sticks with you. It doesn't go away.
Un arrepentimiento es cuando miras atrás algo de lo que tenías control, de lo que tenías cierta potestad, que tenías cierta potestad y no hiciste nada, hiciste algo malo y se te queda, no desaparece.