I may be in this a little too deep, but this is my opinion. There IS, in a way, a Heart of the Cards.
One day a jerky new kid with Duel Monster cards moved to my school. I was outside Dueling a 5th grader and the guy came up and stole my Cosmo Queen, put it in his deck, shuffled it well, and challenged me to a Duel for it. I whipped him pretty badly. In my first hand I had Seiyaryu, Dark Magician, La Jinn, Monster Reborn, Soul Exchange, and I drew the Field card Yami. When I took Cosmo Queen out of his deck it was at the very bottom. I'm serious!!!! My cards won't work for anyone else! I let my best friend borrow my cards for one Duel and he got creamed badly. All of my best cards turned up at the very bottom. Now how's that for a good example?!?!?!
In Yami's words, "I doubt you have that kind of faith in your cards."
Honor-wise, an honourable Duelist is one who is willing to Duel for what is right, no matter how hard the chalenges may seem. To Duel with honor is to Duel with wisdom, courage, and a trust in the Cards.
I rest my case. *walks away into the shadows*