Music theory is very organized. Good musicians who have studied how music is put together know a whole bunch of common chord progressions. Especially with blues/rock. If you are sitting in with some peeps and someone says “blues in E” everyone knows what the musical structure is going to be. With rhythm, it’s similar. If it’s a rock song everyone just gets into a rock groove. Music repeats. Once someone lays out a pattern the others listen and fall in pretty quick.
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