So the question becomes, can you train heart?
Yes, if you have the right experiences you will develop heart. I don't think it's easy though. I'm not sure that it's for everyone either. Most people are in martial arts to learn to beat someone else up, not learn how to take a beating.
Can you imagine saying to a prospective student "Well the first part of the training involves getting hit until you get used to it, then we'll teach you how not to get hit?"