In The Teachings of Don Juan, Don Juan tells this word for word to his student Carlos. He follows it up by saying only an older, wiser person is likely to understand what it means. He said when he was young he was too full of passion and fire to understand what it means and that not until he was much older did he understand what a path with heart was.
If you ask yourself if a path has heart and it does, you will know for certain. Perhaps you are uncertain because you want to follow a path for egoic reasons that is heartless for you.