Note values & subdivision

There's room between two counted beats. Saying "1-and-2-and-3-and-4-and" fills it audibly.

Rhythm is essentially the division of the same beat. A beat can be held, halved (the "and"), or quartered; the finer the division, the busier the pattern, without the underlying tempo changing. The counted number stays the framework; the subdivisions are what happens in between. The "and" is the most important of them, because groove is built on it.

What matters is the insight, not reading notation: a fast pattern and a slow one can share the same pulse — one just divides the beat more finely. Feel the one securely, add the "and," and you have the grid every strumming pattern moves within.