Ingest pipeline processors what constitutes a failure?

If i use an ingest pipeline with a processor of some kind say an enrich processor and i provide a valid enrich policy with valid fields to match and enrich. If no match is found i assume this would not constitute a failure? It would ignore and move on to the next part of the pipeline?

Is there a format that would give me essentially an onNoMatchFound(do x (set field 'match_found' to false)) (i know this isn't a property of the enrich processor but im looking for a pipeline setup that would act in that way)

Or am i not understanding onFailure() correctly?

Apologies if that does not make much sense.

Cheers