TRACE stands for Trace, Read, Analyze, Codify, Enforce. This lesson teaches the first two steps, which are the most important, and which are squarely product work rather than engineering, this is your part of the loop, not something to wait on an engineer for.

Trace means capturing what your product actually did. A trace is the full record of a single interaction from the user's input through to the final output, including any steps in between. You cannot evaluate what you cannot see, so the first move is always to collect real examples of your product in action, a sample of actual interactions, not imagined ones. If you have no real usage yet, you generate some by using the product yourself across realistic cases.

Read means doing exactly that, reading through those traces, one by one, and noting what went wrong. This is deliberately low-tech and it is meant to be. You sit with, say, twenty to fifty real interactions and you journal: for each one, what is good, what is off, what failed. No metrics yet, no tooling, just a human who understands the users looking honestly at what the product did and writing open-ended notes. This is borrowed straight from qualitative research, and it is the single highest-value activity in all of evaluation, because it shows you the failures that are actually happening in your product, rather than the generic ones a tool would guess at.

Why is this your job specifically? Because reading traces is about judgment, knowing what "good" means for your users and your product, and that is product thinking, not engineering. An engineer can build the machinery to measure a failure, but deciding which outputs are failures in the first place requires understanding the user, which is you. This is the lesson's real point: error analysis makes you the owner of quality, not a spectator waiting for the technical team to tell you how the product is doing.

You will read your own capstone's traces live and start your own list of what is going wrong. That list is the raw material for the next step.