Q: Why was no brains written in F# major but performed in Bb major?
A: because when i wrote it, i was either not singing, or not singing at full volume. Before starting production, it's normal to do a 'key test', where i check how it feels to sing it at full volume, and find what key is best. that's when the production key of a song is determined, and it's all based on what key is best to sing it. it's common for the production key to be a few steps higher than the writing key, because as i'm writing i'm probably singing it quieter and not as intensely, therefore probably in a lower key for writing