Being a skilled warrior does not come naturally. It requires rigorous training with weapons and magical signs. However, those are quite dangerous, as you can cut yourself or people nearby. The magic is especially dangerous in the hands of unexperienced users. You could accidentally blow up your aunt, or put the wall on fire as this video from Witcher 3 mo-cap demonstrates.

Fortunately, the damage from Igini sign was limited and the fire extinguisher was nearby. If they had been recording duels, the accidental Igni or Aard would have put his partner in the hospital. Do not try learning magic at home, only do so in well-prepared facilities.