You're very unlikely to always get your work accepted for everything you try for.
You're very likely to be subjected to the occasional let down.
When you find out that a customer doesn't like your work. What do you do? Do you sulk? Do you complain about them and say that they were impossible to please, do you shrug and move on to the next project?
I think you should always ponder whether or not your work was your best. Do you need to learn from it and work harder? Sometimes they are just difficult to please but every experience should nurture your writing talent or at the very least, should teach you something about your craft.
Today I endured an experience that taught me that I will deal with the occasional rejection. At first, I felt the sting but then learned a bit about why my work was rejected and learned a bit about how people that I work with feel about me as a writer and it didn't seem so bad.
I have decided that it was inevitable for me to experience this but the way it happened was actually positive because two compliments came out of the rejection so I did get the blow rather gently. It was kinda like being hit with a pillow extra hard. It hurt a little but was kinda funny at the same time.
So here I sit with my hair a little mussed but I dusted myself off and I will soldier on.