This article is another view on the skill of learning how to handle rejection of your writing (see my recent post here) Terri Giuliano Long describes her own experiences, and that it is important to separate ourselves from our work:
Conflating self and work shifts the emotional emphasis from work as a product of labor to work as an expression of our personal identity. Acceptance or rejection, criticism or acclaim – these subjective, often idiosyncratic, judgments become an assessment of us. Great when the assessment is positive, not so great when it’s not.
She describes how she spent many months focussing on the single project she was working on, and when it fell through for reasons outside of her control, it felt like a personal rejection of her effort, and with no other projects lined up or ready to go, it was very hard to stay motivated.
Have a look at her coping strategies for getting enough distance between her work and her identity so you don't drown in the never-ending waves of rejection. And yes, they are never-ending.