To all you PitchWars hopefuls, I'm sure this question has crossed your mind, especially now since the Mentee announcements are on the horizon! So let me give you an answer, because I've been on both sides :)
Before I get into it, I should mention that my answer is based on my own experience. Ask another mentee and their answer could be different. But here's my perspective. I hope it gives you some insight and motivation to keep writing.
When you don't get in...
In 2014, I applied to PitchWars for the first time with a fully revised manuscript (M1). I spent about a year on it going through multiple drafts and making it the best it could be. I connected with other hopefuls on twitter, submitted my entry, stalked the mentors (hoping they were talking about my awesome manuscript), and waited and waited for the announcement to finally come.
Once it did, I did 'ctrl+F' for my name. Nothing came up. I read the list from beginning to end, the rejection slowly sinking in. This feeling of disappointment and not feeling like you're good enough, the doubts, they hit me all at once. I congratulated the other hopefuls who did make it, but then I kind of disappeared from Twitter (granted, I never really did use twitter much anyway back then, so NBD).
But I still felt my MS was ready, and PitchWars pushed me to prepare my materials for querying, so I did.
More rejections resulted, until I finally came to the realization that this MS was not the one. So I shelved it and started another MS. We'll call it M2. I worked on it all fall and winter, but something was lacking in the story, so I quit halfway through. It took a vacation and a new perspective for me to sit down and try again. I started M3 at the end of April and drafted it in six weeks, quickly revised based on my CP's comments, and entered it into PitchWars. This time, I got in (more on that below), but I probably wouldn't have if I didn't keep writing.
So what do you do when you don't get into PitchWars?
You keep writing, pursuing your passion, and continuing to improve your craft. In a span of one year, continuously writing, reading, and learning from others, my writing improved so much and it showed in the manuscript that got me in.
One thing I will critique myself on is the fact that I left twitter. Twitter is a great place to meet other writers and to just connect with people who are passionate about writing, reading, and books in general. Find your CP's, your betas, your tribe. This creative path we've chosen to pursue is an arduous one, but it'll be so much better when you have someone alongside you, who gets what you're doing, and understands what you're going through.
So write, write, write. Connect, connect, connect. Read, read, read. Learn, learn, learn. Got it?
And when it comes to rejection, know that it is part of the process. Rejections may hurt, but they're also a testament to your hard work. You're doing, you're trying, and you're putting yourself (and your work) out there. If you keep at it, you'll eventually get to that 'yes' you've been working toward.
When you do get in...
In 2015, my name was on the mentee list. I was shocked. I cried. I forgot to make dinner. I celebrated. It was amazing. I got my edit letter from my mentor, and then came a lot of hard work.
You write, write, write. Revise, revise, revise. Read, read, read. Connect, connect, connect with your fellow mentees. And you learn, learn, learn from your mentor. In some ways, getting in is similar to not getting in; both involve persistence, growth, and working your butt off.
Except instead of querying right away, you have the agent round first, and then you start querying.
Then come requests, maybe an offer of rep, but also rejections.
No matter where that manuscript that got you into PitchWars leads you, know that it's never over. You'll still have to write another manuscript, you'll still have to work on your craft. You'll still have to create, revise, and edit. Because that's what writers do. We write. Whether you get into PitchWars (or any other writing contest for that matter). This goes without saying even if you aren't/are agented/have a book deal.
I will say that PitchWars is a pretty amazing opportunity, so if you do get it in, cherish the experience, work hard, and give it all you got. But if you don't get the opportunity, do not be dismayed. One contest is not the end of the road for you. We all take different paths to get to our dreams. So whatever happens, you are awesome. You wrote a manuscript, you had the guts to try, and you'll continue to write because you love it, because it's part of you. Take heart, and persevere.