Lucy raised her wand and she said : " Professor I think that this Rune could enhance the effect of the spell:" Protego". The wizard who uses this spell is protected by a shield that defends him by the attack of his enemies but meanwhile the wizard has the time to think about the next incantation and he can increase his concentration.. If the wizard hasn' t the willpower or he is not focused on the sign the shield can be broken by another spell"