Pink Has Stated That "Who Knew" Is About "the Death Of Friendship. You're Best Friends Forever And Then Three Years Later You Haven't Seen Each Other In Two Years — What Happened? You Grow Apart And People Come In And Out Of Your Life For Different Reasons Seasons." She Said In An Interview With The Observer That The Song Was Written About Friends Who Died As A Result Of Drug Overdoses. According To Her The Song Is About More Than One Person "There's A Couple Of Different People Mixed In ... It's Just The Grieving Process. You Can Look At Somebody He Might Be Right There And The Next Monday He Might Not Be." In An Interview With The Television Station TV3 She Said That "... She Always Wanted To Write A Song About Death Because She Came In Contact With Death At A Very Young Age". Billboard Magazine In Its Second Review Of The Song To Accompany The U.S. Re-Release Called It "another Cool Smart Plenty Passionate Melodic Jewel About The Death Of A Friend And/or Friendship With An Instantly Identifiable Quick-To-The-Point Singalong Track—maintaining Pink's Stance As The Smartest Female Millennium-Era Singer/songwriter Dazzling In Star Quality As Alterna-Pop's Premier Princess." The Song Features Acoustic Guitar Keyboards Drums And Electric Guitars. Gottwald Martin And Pink Co-Wrote Another Song On The Album "U Ur Hand".