Disagree about it being a rookie mistake. In the simple case, yes. But consider data used by an effect could travel all the way from root to the max depth of your tree with any component along the way modifying it, potentially introducing unstable references. Maybe it worked when you tested. But later someone introduced a new component anywhere between data source and effect which modified the data before passing it on. That component may have used useMemo. So it looks ok, but it over fires.

You become reliant on all your ancestors doing the right thing, in every situation, forevermore. One mistake and unstable references cascade everywhere. The surface for introducing errors is huge, esp in a large, complex codebase. And we have no way to guarantee a stable reference.

>But consider data modified

This is why we never modify data but create new data. Data must be immutable. Strictly typed. Always in the form it is expected to be. Otherwise - crash immediatelly.

>But later someone introduced

This is why we write integration tests. Introducing anything without tests is only guesswork.