eli5: why do we know a note is off key even when we’ve never heard the piece of music before?

Question

Whenever I hear someone play an instrument, I can always tell when they’ve played the wrong note even if it’s my first time hearing it, why is that?

In: Other

Answer 1

Are you asking about off key, or the wrong note? Off key generally means what you hear is akin an out of tune instrument. Pianos, guitars, violins, etc allow the tightening or loosing of the strings to put notes on key.
The so called wrong note means that it wasn’t the note that the listener expected. In reality, sometimes it is the wrong note, but occasionally the composer intentionally surprises the listener.