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Both require the learning and manipulation of abstract symbols whilst performing 'in the zone'. Programmers and musicians both learn to weave these abstractions into a larger, continuous tapestry. Musicians stream notes into music, as coders stream logic into a program.

However you'll also find it usual for excellent people to excel in many areas, so the real question here is - How many professions do you have in your circle of friends? I would expect there to be similar correlation of musicians in any other occupations which require timing, dexterity and creativity.