 "Si Una Vez" is written in the key of D minor and is played in a moderate groove of 84 beats per minute. It incorporates music from several musical instruments, including the piano and guitar. Lyrically, Selena reminiscences her failed relationship and wonders why she ever fell in love with an abusive partner who betrayed and left her, vowing to never allow a man like that back into her life. The lyrics suggest unrequited love and female empowerment.
