String interpolation is magic because it's not entirely obvious when it happens, what scope rules are followed, if there are any side effects, if the original string is overwritten or whether a new instance is created, what happens when they are used within bodies of loops, what happens when they are used within closures etc., it just works. Sure these can be specified explicitly but they aren't obvious.
It's the kind of feature that is useful when you write an application but not that useful when you're trying to debug it.
