Magic takes up energy to use and everyone based off genetics or extensive training or maybe even drugs has a certain amount of Mana. Mana is the body's attempt to control your souls innate power and depending off the factors I listed earlier, you can have either small or large amounts of it. But you also have to be able to conserve your Mana and use it efficiently even if your Magic takes up a lot of it. The Divinus have a different version called Divine Energy which depends on their family.