Here's what I find interesting about this. When you know your material really, really well, you can deliver a performance while doing other things. But this level of multi-tasking is impossible unless you are totally prepared.
The first time I recall being aware of this was when I sat in the front row at a Rolling Stones concert at Fenway Park in Boston in 2005. During Satisfaction, Ronnie Wood was playing right in front of me (see photo) while chatting up the cute girl right next to me: “Hello Love!” Ronnie said. “How are ya?”
Do you know your stuff so well that you can multi-task?