I've heard guitarists tell me "Even if I've never heard the song, if I know it's key, then I can usually play through it O.K" There's a term for it, I know. Anyways, I understand the concept of keys, intervals, etc. But, what exactly is going through the minds of these guitarists when they're playing that allows them to do this? A few notions that come to mind are: 1. 95% of songs start on the I chord of the key. So, you can bet if it's in E minor, it will start with an Em chord. 2. There are conventional chord progressions for each given music genre. So, you can bet that if it's blues, there will be a IV and V chord in there somewhere after the I. I guess my question is, with my knowledge of music theory, and good memory of note location on the fretboard. What exactly should I be thinking after the guitarist yells out "We're in A" and it's time to start playing a song I've never heard before.