Everyone needs the essential vitamins and minerals. Back in the day, sailors on months-long voyages used to find out the hard way how vital these vitamins are. No vitamin C = scurvy. As a result of evolution, humans long ago stopped making these essential nutrients and outsourced the work to plants and animals. But the nutrient manufacturing got split across a wide array of plants and animals, so we are forced to eat a variety to get everything we need. Even today, many of us struggle to do so (Curse you, outsourcing)! Because the outcomes of nutrient deficiencies are so unfortunate, a great deal of research has been done to pinpoint how much of each nutrient we need. These recommended amounts are referred to as "Dietary Reference Intakes." [NIH]
To add another layer of complexity (thanks, nature!), our genetics can affect how much of the nutrients we need. Genes have been linked to an increased deficiency risk for nearly every essential vitamin and mineral. People with these genes are likely to need a bit more than the standard "Dietary Reference Intakes."
These two layers of information are combined to generate your personalized recommendations.