Why do Horseshoes mean Lucky?

I have received a very interesting coin recenetly. It is a coin in a horseshoe shape.

Some people may see western people hang horseshoes over their doors of the buildings. Someone like me would like to ask the reason behind this little thing. Why horseshoes?

Let me share you a story about hanging horseshoes over the doors.

This story is about a hermit – St. Dunstan.

St. Dunstan was a very quite and humble hermit as well as skilled metalworker. He lived in a hut where near the church of St Mary.

One night, there was a Devil came to his hut as a woman. However, St. Dunstan vigilantly noticed that he was a Devil instead of a woman. He saw his cloven hooves beneath the dress he wore. Dunstan noticed that the Devil was limping on one of his cloven hooves. He pretended to offer a shoe to help the Devil. He then nailed a red hot horseshoe onto the Devil hoof. 

The Devil screamed and begged St. Dunstan to take it off. Of course St. Dunstan was not going to do it easily.

He said, “You have to make a promise that you will always respect the symbol of the horseshoe and never enter a building that is protected by the sign of a horseshoe.”

Nowsdays, people are still telling about this story to Children in England. And hanging horseshoes over their doors have become one of their tradional. Also, people have different preference about hanging heel up or Down.

Some says that if you hang the horseshoe like a shape of a cup, it means horseshoe fills with good luck, holding it for everyone who lives in that house. 

Some says that if you hang the horseshoe downward, it means good luck flows out from the horseshoe and onto all the visitors and family who come into that house.

Up or down? Which one do you prefer? Let me know your thought.