Patronus

In the story of Harry Potter, a Patronus Charm, which can fight against the Dementors, is a kind of advance magic. One can only perform a proper and strong Patronus Charm with the support of a happy memory, not just a piece of ordinary happy memory but the happiest moment one ever had.

“Dementors” are quite common in our daily lives and they may find us without signals (not even the coldness or darkness mentioned in the book). Story is just story but you can still explore something practical from it. I finally realized it’s true that the happy memory or the positive feeling is undoubtedly a powerful element to cast the spell - and the most important - to protect myself and people around me from the attack.