Why must a microscope stage move in very small increments at high magnification?

A microscope stage must move in very small increments at high magnification because the depth of focus of an objective lens decreases as its numerical aperture increases.1

For high-magnification objectives, this depth of focus can be as small as 1 or 2 micrometres. Consequently, the mechanical components of the microscope must provide stable, precise motion at increments even smaller than that depth to ensure the specimen remains in focus. If the stage or focusing mechanism lacks this level of precision, it becomes impossible to maintain a clear image, as the narrow range of focus would be easily bypassed by larger, coarser adjustments.12