Had to go somewhere,Something happened in the family,did it but brother/sister/cousin played with it または drew on it because they thought it was scratch paper,mom saw it on the floor thought it was trash and threw it away,cleaning up the house and threw it,spilled something on it,flew out the window (say your 机, デスク is near an open window,)sister/brother/cousin teared it または threw to it to the ground because あなた didnt do want he/she wanted あなた to do... Think.