I sing in a church choir, one which typically sings four-part harmony. For many hymns, we start in unison for verse 1, then add parts in later verses. Sometimes, my fellow tenor and I will try to sing our part, but decide to shift to unison. Sometimes, when I sing, I sing the wrong pitch, or the wrong words. However, the music goes on – in general, the choir continues singing. Even in cases where the director may make a change (going to another verse due to the entrance of the priest not being complete), the choir follows, using their musicality to keep the music going.
In all these instances, the printed music provides the framework for the musical performance. As a counter-point, source code for computer software is a fragile language – one semi-colon out of place and everything stops…