You Never Can Tell is an 1897 four-act play by George Bernard Shaw that debuted at the Royalty Theatre. It was published as part of a volume of Shaw's plays entitled Plays Pleasant.
The play is set in a seaside town and tells the story of Mrs Clandon and her three children, Dolly, Phillip and Gloria, who have just returned to England after an eighteen-year stay in Madeira.
The children have no idea who their father is and, through a comedy of errors, end up inviting him to a family lunch. At the same time a dentist named Valentine has fallen in love with the eldest daughter, Gloria. However, Gloria considers herself a modern woman and claims to have no interest in love or marriage.
The play continues with a comedy of errors and confused identities, with the friendly and wise waiter, Walter (most commonly referred to by the characters as "William," because Dolly thinks he resembles Shakespeare), dispensing his wisdom with the titular phrase "You Never Can Tell." (wikipedia.org)