Why do We Sing the Bad Note

I am sitting in a room where the chairs are encircling a piano. I feel a soreness to my throat and realize I might be getting sick. Looking outside I see the storm coming closer and the black clouds rolling in. With the approaching storm I feel the room getting colder and colder. I then realize more students are coming in the room and I feel my palms start to sweat and I start to get a little nervous. Today I will be singing a solo at the beginning of class. As I begin singing, there are no problems but then half way through the song I think of all the influences around me and I sing a bad note and not just one, but two or three. The sore throat, the approaching storm, the cold room, and the nerves are all influences on the bad note I sang during my solo. After hitting the wrong note, I did not want to finish the song but I kept going. When I was done singing I left the room and the outcome of the bad note showed anger at myself and the music, but on top of the anger I was really embarrassed. I had worked on this solo for a very long time and knew the notes but for some reason they notes came out bad. I had just decided the bad note also gave me the outcome of retiring from my solo career and to just stick with choral singing.