The song title "My Greatest Mistake" could easily refer to one pianist named Jack O'Brien being mistaken for another -- it certainly couldn't have anything to do with the song itself, seeing how it was recorded more than a dozen times by some of the greatest jazz artists. Such a strike of ore was what every songwriter and piano tinkler such as O'Brien focused on each morning upon descending into the Tin Pan Alley mines. This stands in contrast to another Jack O'Brien, who worked as a pianist in jazz bands in a variety of parts of the world during an overlapping time period, but mostly as a sideman and apparently with hardly a songwriting dabble.
"My Greatest Mistake," written in collaboration with the prolific Jack Fulton, is apparently the most famous song O'Brien has ever been associated with. His entire catalog includes "Thumbs Up," a 1941 effort for which his collaborator was tunesmith Bert Lown; this was the official theme song of the British War Relief Society. As a pianist, O'Brien's collaborators included Ted Weems and Glen Carr, the latter an orchestra director trying to make "My Greatest Mistake" his signature song. Piano credits connected with bandleaders such as Lud Gluskin and Enoch Light belong to another O'Brien, active in the New England area throughout the '70s.