 " 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 . 
