Any code that calls arbitrary callbacks is prone to failure. The context in which a callback is called matters. Calling a callback at the end of a method avoid

Any code that calls arbitrary callbacks is prone to failure. The context in which a callback is called matters. Calling a callback at the end of a method avoids interfering with the caller's state but ignores the state of the caller's caller. An ethereum contract will only be tractably analyzable if it avoids dynamically invoking arbitrary callbacks.