It’s happened to us all. We received an email from an editor that dashed our hopes and dreams against the rocks. Rejection is a fact of life and even the most successful of writers have gone through it several hundred times, Stephen King, Ray Bradbury, and E. E, cummings to name a few. Today’s publishing market is not as ridged as it once was. Now there are other avenues for writers to seek publication such as online-only publishing, self publishing, or paying to publish but the old publishing houses remain and rejection letters are still given out in healthy doses. An interesting topic to explore might be the sudden drop and forced recovery after receiving a rejection. You could use numerous examples of people who have survived and give helpful hints and tips for those feeling discouraged. In the words of Sylvia Plath "I love my rejection slips. They show me I try."
As you say, Stephen King, in his part-memoir part-creative writing course "On Writing", relates how he used to poke his rejection slips onto a nail in the wall above his desk. Eventually the nail bent under the weight. He carried on writing anyway, and with each rejection slip learned something new and to try harder and stretch his talent further. – ThomasB1 month ago