A lot of men have fantasies about being a slave and those fantasies usually women as being a mere erotic image, a leather clad goddess who will satisfy their every kinky desire. The fact that she is a flesh and blood person with needs and desires of her own never really enters the equation. The potential slave always claims to have no limits and when he is with her he is constantly waiting the moment when she will fulfil his desires.
But being a sub or a slave is not a fantasies- yes fantasies can be fulfiled- It's a comitment. At least it is to my mind. It's a relationship based on total honesty. If a person is not willing to give that then the relationship just will not work. Like any good relationship it is about what you can bring to the table. What qualities do you have as a person that would make a Domme or Mistress consider collaring you? If you have nothing to offer as a person that what can you offer as a slave. The parts of you as a person and the parts of you that contain the slave heart need to blend together as a whole.