play it by ear

decide what to do as the situation develops

• I haven't planned the trip in detail — we'll play it by ear.
• I'm not sure how long the meeting will last; let's play it by ear.
• We don't need a strict schedule for the party, we can just play it by ear.

This idiom is used in informal contexts, often in everyday conversation to convey flexibility or adaptability. It's common among native English speakers who want to keep their options open and not be tied down by a rigid plan.

A common mistake is translating it literally from the Spanish 'tocar de oído'. While it might seem similar, in English it refers to adjusting plans according to circumstances, not playing music without sheet music.

• the proof of the pudding is in the eating
  the real test is in practice, not theory
• leave no stone unturned
  make every possible effort
• the writing on the wall
  clear signs of impending failure or change
• throw caution to the wind
  act recklessly, abandoning prudence