This is how you survive rejections. As writers, we get to experience many of them, and it will often take years to get our acceptance letter. But with the right mindset, you can accomplish anything. 

Firstly, I want you to remember two things:

1. Your writing isn't garbage. In fact, it's most likely great stuff. There's nothing wrong with your writing ability, that's not why you keep getting rejected. It keeps being rejected because it just wasn't right for the agent/book publisher at this specific date and time. Repeat those sentences until they fully settle into your mindset: There's nothing wrong with my writing ability, and the publishers/agents keep rejecting my manuscripts because they're currently looking for something else.

As the publishers never tell us what they're looking for, we just have to keep playing the guessing game with them and send in our beloved writing willy-nilly. Keep sending your writing to publishers and eventually, you'll get a "yes". 

2. The most personal thing you can ever give to another person is criticism. This is because it tells more about the other person than it does about you. For example, if someone tells you, "You're garbage" then you're definitely not. It's those who say that about you who are not a very nice person. Think about it, and you'll discover more and more how people reveal their most sacred to you when they give criticism. 

As you're going to go through hundreds of no's, you need to prepare yourself mentally for it. Having a great writing community online helps a great deal with being your support group. Many of us writers have experienced that the people around us are very poor at providing us with the yearly long stamina that we're going to need to survive rejections in the book industry. Some of them mean well, as they don't want you to suffer. Others just don't understand what it is you're fighting for. And in another camp, you find those who just don't have your best interest at hand. 

You find the writing community by using the hashtag #writingcommunity on your social media apps. 

If you prepare yourself for that it will take years, and you're going to go through hundreds of rejections, your mindset is going to adapt to it. In the US, I recommend you get an agent first. I know of those writers who have queried 200 agents until they've found their perfect helper. The agent will then try to sell your work to book publishers. In the UK and Sweden, you query straight to the book publishers. They're not as many, too. I don't know about the rest of the world, so sadly you need to find that out elsewhere. 

The last piece of advice I can give you is to roll with the punches, take comfort in the writing community when it gets hard (because it is going to get very hard), and keep writing! Never stop writing! Somewhere in your head is a manuscript that's going to be accepted. Keep looking for it! 

All the best of luck and keep fighting for your dream of being a published author! 

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PS! Don't frequently send in the same work to the same book publishers/agents. If they've said no, it will still stand years from now. Accept it and move on. If you haven't heard from them in three months, a no answer equals a no.