How does it happen? Once your Soul is ready, it attaches to a specific newborn that was created specifically for your soul, for each physical life is fated on your soul, meaning every event was fated, your reactions however are not fated. Do not see physical life as ending and restarting, for the physical life is but a means to an end. Your life is the existence of your soul, being reincarnated is comparable to when a crab leaves one shell and obtains a new one.