This log exists because action outran certainty.
Pianotrainer started as one site with a consistent visual shell and a clear information architecture:
One coherent product. Clean structure. Clear intent — for users and for bots.
Then the site changed. Not in one dramatic pivot, but through a sequence of real building.
A new toy appeared — Path of Harmony — showing chord shapes on a chromatic circle. That led to cinematic two-chord movement. That led to Two Paths of Harmony: Flow and Color. That led to emotional progressions and guided practice.
None of these steps were wrong. They were productive. They were exciting.
The system grew faster than the signals.
More pages. More concepts. More possible audiences. Still very little feedback about what actually mattered.
At that point, the biggest risk was no longer a bad feature. It was getting lost.
The decision that followed was to split PianoTrainer into three separate products: Pianotrainer, EmotionalChords, and MusicalToys. At the time, this split was driven by iteration and momentum, not by explicit thinking models or formal reasoning.
Behind the Build exists for moments like this.
From this point forward, decisions are logged when they are made and left intact. If the world changes, the decision is not rewritten — it is revisited through a new entry.
When reasoning needs structure, a small set of mental models is used. These models were chosen not to be clever, but to avoid getting lost: they help surface blind spots, limit damage, and keep decisions grounded when signals are weak. Not every decision needs every model — only what meaningfully reduces confusion.
This is how motion stops being confused with direction.