When I was a wee little 22-year-old poet I was roommates with a journalist and writer in her late 40s. She treated my writing ambitions seriously, and we often talked about writing. When I got my first rejection from a literary journal I called her. I felt good, and she summed it up.
“Congratulations! You’re a real writer now!” she said.
I got my first agent rejection today. It hadn’t even been 24 hours since I had sent the query. When I saw her email my heart jumped. Of course it did. But I wasn’t surprised to read her “not a good fit, best of luck placing it elsewhere” note.
She represents mostly fiction (I subscribed to Publishers Marketplace, which I highly recommend in order to find out what each agent really represents). Her blurb said she was looking for nonfiction, even though all her sales were romance novels.
Resilience is one of the most important characteristics for a writer. I am not always a resilient person in the rest of my life, but I guess I learned young with writing.
Fangs and Clause 
It only takes one yes. keep at it.
Oh, my goodness, those “not a good fit, best of luck placing it elsewhere” notes. I got one that actually told me she thought it was probably something she might have liked, but the current political situation left her too sore to approach. (My novel began with a death.)
I am not one of those who keeps my rejections, though I do agree, it is a rite of passage, something to learn to get through. I did keep rejections for a time, back when they were paper, but file and try to forget them.
I keep my rejections to be able to share them with my students and give them courage. Indy and I stumbled across our dad’s rejection letters when we were tidying up his papers. I am so glad I did!
I do not keep the rejections! But I do acknowledge them as they come.
I’ve received my share. Last week I received both an acceptance and a rejection for the same story at the same publication. Still not clear how it stands.
That’s worth a follow-up email for sure!