Strumming patterns — the pendulum

Let your strumming hand swing steadily up and down over a chord loop, hitting the strings only some of the time, and groove appears. Stop the hand between hits and the same pattern sounds stiff.

A strumming pattern isn't a set of individual strokes, then, but a continuous pendulum: the hand moves steadily up and down in eighth-note pulse. The pattern only determines which swings hit the strings and which pass through empty. Downward hits fall on the count (down, ↓), upward hits on the "and" between them (up, ↑); the ones that don't connect are ghost strums.

That contains the actual point: a pattern stays in time precisely because of the empty swings. Since the hand never stops moving, it's automatically in the right place for the next hit. This is also why strumming direction isn't freely chosen — it's tied to the position in the count. What's free is whether a swing connects; forcing the opposite direction works against the pendulum.