A subpixel on an LCD can only have a single brightness value across its whole area. The dots or stripes on an CRT have no such restriction, they are effectively

A subpixel on an LCD can only have a single brightness value across its whole area. The dots or stripes on an CRT have no such restriction, they are effectively little monochromatic pictures themselves. Don't think of those dots as fundamental elements of the image, the CRT doesn't address them and doesn't care about their shape. They are really just a color filter on top of the three greyscale images projected by the electron gun. The shadow mask ensures that each of those three electron streams land on the right color. See the TechnologyConnections video for more details.