It is one thing to cast hexes when no one’s interrupting you, but another if you’re trying to do so in the heat of battle. You have to be able to concentrate on the words dancing on your lips and not worry about someone gutting you with a sword.
This is why it’s crucial that you add a short incantation to the first hex you decide to conjure when entering a fray: 'Pazuzu, may the south wind protect me!’. Thus, the demon lord will accept your blood offering and grant you a bit of safety – a thin, invisible barrier shall appear between you and your foes. Still, be mindful that it is not impenetrable. It might give you some breathing room, but it will not hold forever.