You are absolutely right on this matter @the-lead. Yesterday in Church I had similar issues. Given that it was mothers day, the women is our church covered the Mass. They invited me to play the keyboard for them and I did. Apart from the fact that they were an amateur choir, one of the song they rendered was not well learnt. They completely messed up the song, and I did too. I completely had no idea of the song myself, and it was not a song with a stable progression.