Manifesting Desires and Fantasies

I am battling to fully understand the difference between my true nature desires and fantasy.
If nature wants us to have all abundance and wishes to fill each of our desires, how does the fantasy nature of a desire separate it from this state?
For me fantasy is a desire removed of all limits and boundaries, a wish that envisages no fear. So then why would this fantasy not be deserving of manifestation?
I am confused as to the limit of which needs and desires are attainable and which are not?

I would greatly appreciate your insight to help me better understand the topic.