Kindness, with a confidence-boosting lesson. The key to raising Ponymon is friendship and respect.
"Believe me, Twilight. Never feel discouraged by losing. It's only truly a loss if you've learned nothing from it once its over. Even your teacher, Princess Celestia, in all her immortal wisdom and power, has lost battles before. In the end, it's not about how many times you can win. It's about how many times you fail and keep moving forward; how much you can take and keep moving forward. We're not always going to win. But as long as we can pick ourselves back up and learn from our losses, we can get stronger. That is how winning is done!"

Hmm, I say we be kind:

"There is no point in lying down when defeat stops us in our tracks. We stand up, and we keep walking, because together, there is nothing we can't overcome".