Well, the failure in question is not the part failing to do what it is objectively defined to do, it is a failure to perform as we expect it to. Meaning, the failure is ours. Inductively, for `x` to FAIL means that either we failed to define `x` properly, or the `y` that simulates `x` (compiler, whatever...) has FAILed.

Of course, the notion of "failure" itself presupposes a purpose. It is a normative notion, and there is no normativity without an aim or a goal.

So, sure, where human artifacts are concerned, we cannot talk about a part failing per se, because unlike natural kinds (like us, where the norm is intrinsic to us, hence why heart failure is an objective failure), the "should" or "ought" of an artifact is a matter of external human intention and expectation.

And as it turns out, a "role in a system" is precisely a teleological view. The system has an overall purpose (one we assign to it), and the role or function of any part is defined in terms of - and in service to - the overall goal. If the system goes from `a->d`, and one part goes from `a->b`, another `b->c`, and still another `c->d`, then the composition of these gives us the system. The meaning of the part comes from the meaning of the whole.