Not an exact quote, more like an opinion, a thought. Dementors suck out happiness from people. The make people remember their worst moments in life. The way to defeat them / repel them is to cast a patronus charm, [incantation: expecto patronum. If my latin serves me right it means I expect / I command my patron].The difficulty lies in casting the charm while those foul creatures make you feel terrible and the charm only works if you can conjure up a most happy memory.I suggest a new / additional interpretation of JK Rowling's idea:Demen - tors are your inner demons that make you feel terrible, things you did in your life, terrible losses you experienced (Harry hears his mother's screams) and negative emotions.Those inner demons TORment you and your soul. You can only escape those horrible impressions with an overwhelming positive force of imagination. Happy moments in your life, thoughts about friends, family, love and connection versus the horrible loneliness that your inner demons create.
~ Thomthor
