The fine-tune that learned the voice and lost the knowledge
You fine-tune a 7B base model on 4,000 internal support transcripts so it answers in your company's house style. Three epochs, learning rate 1e-4, full fine-tune, batch size 8, no scheduler.
The result writes in exactly the right voice. It also now claims your product supports features it does not, cannot do arithmetic it could do before, and answers general knowledge questions confidently and wrongly. Training loss fell smoothly throughout and validation loss on a held-out slice of the transcripts is at its lowest.
A colleague suggests training for more epochs on more transcripts.
Name the failure mode precisely, explain the mechanism by which this specific configuration produced it, and tell me why the validation loss is not just uninformative but actively misleading here.
Choose how you want to be interrogated
The same case under two modes is two different exercises. If you are unsure, RCA drill is the one that trains root-cause analysis most directly.
RCA drill
A symptom, and nothing else. Find the cause and prove it.
Trains: Hypothesis generation, ranking by prior, and naming the test that discriminates.
Red team
You propose. It attacks. It is trying to make you wrong.
Trains: Defending a position under pressure, and noticing when you should concede.
Socratic
Questions only. It will never tell you the answer.
Trains: Deriving from first principles instead of retrieving from memory.
Design review
Present an architecture. Justify every trade-off you made.
Trains: Stating what you optimised and what you gave up, on purpose.
Viva
Rapid escalating questions. Ends in a graded verdict.
Trains: Answering under time pressure without hedging.
Integration
Problems that span several domains at once. The hardest mode.
Trains: Reasoning across boundaries, where the cause is in a different system to the symptom.
Before you start: you begin locked. The Mentor will give you nothing — not a nudge, not a category — until you state a specific position and the mechanism you think produces it. Four genuine attempts unlock the resolution. There is no shortcut.