To improvise and adapt one's actions according to circumstances as they develop, rather than following a fixed plan.
Examples:
- I'm going to play it by ear — they're sensible adults; I'll let them guide the factory tour.
- Without confirmed attendee numbers, we'll have to play the catering by ear.
Origin: From musical terminology, meaning to play a piece from memory rather than reading sheet music.
Synonyms: wing it, improvise, go with the flow