“Play by ear” has infiltrated the English language to mean that a situation is handled in an impromptu manner, not pre-planned. In the business world, I have most often heard it used in the context of events planning and scheduling. For example, “When we get to the conference, we’ll play by ear whether we need two people at the booth or just one.”
The phrase originally belonged to the music world, referring to musicians who played without music. Many of the world’s greatest performers, especially jazz musicians, played exclusively by ear and were not classically trained.
In fact, the world-famous Suzuki teaching method, is based on having children first play by ear, before teaching them to read music. This method was named after Shin’ichi Suzuki who taught himself to play violin by ear after his father opened a violin factory.
So although we might think we are playing it by ear when we show up unplanned to a corporate event, people who really played it by ear were Louis Armstrong, Benny Goodman, Dizzie Gillespie, Charlie Parker, and the list goes on!