Why do not use pure magic

Some peoples would say that I simply intent to sell one use invocations stick, but it’s the only way to preserve the energy of most user. With the sticks, the only spell you have to master is the revocation spell. The mana needed for the invocation is in the stick.
The invocation of a fireball for example is really easy to master, you simply have to join your wrists together and pronounce “Kamehameha” to launch a fireball from your hands. The problem is that if you want to do more than light a fire of dry wood, you need more mana that any normal human can challenge and it’ll leave you without strength.