Consider for a moment the practical ramifications to being illiterate. Not only do you miss out on the pleasures of reading a good book, you can’t follow simple written instructions.
You can’t read the directions on the pill bottle, so you can safely and effectively take your medicine. You can’t cook by following a written recipe.
You can’t make sense of a road map, or follow the highways signs to your destination.
You can’t order off the menu, read your receipt or make a bank deposit without assistance.