What you are training
Reference-track work is the most-recommended and least-practised habit in mixing, because comparing two mixes honestly is harder than it sounds. Louder always wins, so an un-matched comparison tells you nothing. Brighter usually wins on a quick listen and loses over a whole song. And the differences that matter, a slightly more forward vocal, a tighter low end, are subtle enough to miss unless you know what to listen for. This drill plays two versions of a section at matched loudness and asks you to name the difference: tonal balance, dynamics, width, or depth. Each answer shows what changed. Six rounds train the specific vocabulary you need to turn "the reference sounds better" into a move you can make on your own mix.
After this drill, the plan: The daily plan runs this against your own bounce in Mix Check, so the comparison ends in a single move to test, not a feeling.