An atomic unit is the smallest indivisible unit in a given context. It represents the most fundamental part of a greater whole.
evergreen notes are meant as atomic units because they are about one thing. The aim of an atomic note is to capture the entirety of that one thing.
By maintaining notes in their atomic state, it becomes easier to forge connections across topics and contexts. The notes, however, shouldnât become too fragmented; higher fragmentation results in more complex network which might obscure the view of connections between the notes.
This is similar to the Software Engineering idea of Separation of Concerns.