Programming is quite a remarkable activity:
- It has an extremely low barrier to entry
- You don't need expensive equipment
- You don't need to be in a particular location
- You don't need special credentials
- You can finding information / resources just by opening the internet
- You can learn it / do it independently
- It gives you rapid feedback (which can lead to rapid growth)
- It gives you frequent rewards (which gives a huge boost in motivation)
- It's objective and unforgiving (this is a good thing, because it teaches you how to confront reality)
- It's intellectually stimulating
- It's useful in the real world
- Corollary: you can make money or even build a career out of it
- It's badass (or are you telling me that Hackers WASN'T your favorite movie of all time?)
- Electronics (but this is basically still programming)
- Math (lacks "rapid feedback" and "frequent rewards"; "useful in the real world" is also questionable)
- Go, poker, video games (usually lacks "useful in the real world", sometimes lacks "badass")
- Juggling, poi (lacks "intellectually stimulating" and "useful in the real world")
Playing in time, and in key are pretty objective. You want unforgiving, try to sing the Star Spangled Banner out of tune at some event.