It's been years since my heart defect was really at the forefront of my life and my thoughts, constantly controlling what I did or didn't do, where I went, what my plans for the future were. I've had some hiccups, but for the most part the past six or so years have been relatively healthy. I've been able to accomplish a lot that I hadn't even imagined when I was younger. A lot that I now sometimes take for granted and have to remind myself not to.
I am not my heart, but it is a part of me. A very real, very personal, defining part of me. As much as we may not like it at times, the experiences we've had, the parts of ourselves that we wish we could change, the things that we avoid thinking about are some of the things that make us who we are.
These things that define us, that sit inside of us close to our hearts, that we think about when it's late and dark, they are the stories only we can tell. The relationships that have changed us. The past experiences that have shaped us. It's not the old friend whose name you can't remember that becomes a part of who you are, but rather the person whose name still makes you stop what you're doing for just a moment. That relationship is the one that helps define you. That is the story only you can tell.
So as a writer, you don't want to write about just any problem, experience, or relationship that your character has. You want to write about one that defines them, one that, no matter how old they get, is always going to be massively personal to them. You want to write about what changes their life or shapes their personality or makes them who they are. To take an example from the incredibly popular HUNGER GAMES trilogy (which I've only read the first book of, so no spoilers in the comments please!!), part of what makes this story so compelling is, in addition to the characters and setting and plot, the viewpoint and story is one that only Katniss can tell.
And the great thing about writing YA or children's stories is that so much of what shapes us, what defines who we are, happens during these years. Before we have careers, marriages, mortgages. Those are the stories I want to tell, because those are the stories that, when I read them, hit close to home and stay with me long after the last page has been turned.