Dealing with rejection

We all get it. We all hate it and we all have to deal with it.
As a writer, you have to deal with it constantly. If it isn't a publisher/agent or editor saying this isn't quite right, it is a son, sister or neighbour.
But this is how you begin to learn. One of the main things writers have to understand it that nothing you ever write is going to be perfect. Even when you've finished, polished at least four times your manuscript could undoubtedly be improved.
One persons view is going to be different from another's. No agents or publishers are going to be the same. Each has their own personal likes and dislikes. As writers it is our job to find the agent or publisher who loves our work as much as we do.
One problem with writing is that the work you produce may be important to you, you may think it is special and unique, but someone else could have had the same idea at the same time as you but their style suits the publisher and yours doesn't. Don't take it personally. This is a business, however much it hurts. If your writing is good enough, you will find a home for it.
Stick with it and you'll find that place and see your work in print.