One time-axis is the backbone of a second brain — everything dated hangs off it.
Everything dated hangs off a single year to quarter to month to week to day tree. The daily note is an index of the day, not a container; atomic captures land in day-folders; content rolls up along the spine. One predictable axis makes retrieval and AI-enrichment trivial — the assistant always knows where dated things live and where to write them. Cleverness fragments; a spine compounds.
The tax a spine removes is the filing decision. Without one, every dated thing poses a small question — project folder or client folder or year folder? — and small questions asked a thousand times are what kill a system. Not effort: friction. With a spine there's no question left to ask. It happened on a date; the date is where it lives.
The second payoff is the one that matters for AI. An assistant that knows the axis knows where to read and where to write without being told — which is why enrichment becomes cheap and reliable. Every clever alternative scheme is a scheme the machine has to be taught, and re-taught, and will eventually get wrong.
And because the axis is a hierarchy, it summarises for free: days into weeks, weeks into months, months into a year. Nothing is re-derived; each level reads the level below. Cleverness fragments; a spine compounds.