[naasking]

> The statement that it is better to separate data and behavior is far from self-evident IMO, and I would be very interested to understand why this is such a deeply held belief. Seriously, why?

Data is and always has been more valuable and more important than behaviour. It's not unheard of to preserve accounting data that's decades old, even though the accounting system itself changed completely many times. The converse, preserving old programs to run on brand new data is much more rare.

The whole hoopla around big data should make it clear where the real value is. Behaviour is merely a way of transforming data, and coupling the two rarely works well in the long run. The only times it's actually advantageous is to preserve invariants that ensure input or output data is well formed. For instance, data structures that ensure or preserve orderings, etc.