They are the things you get ashamed of because words diminish them -- words shrink things that seemed infinite, when they were in your head, to no more than living size, when they're brought out. When let out it's practically not existing even though you haven't thought about anything else for a long time. But it's more than that.
The most important things lie too close to wherever your secret heart is buried. You can make revelations that cost you so dearly only to have people look at you in a funny way, not understanding what you've said at all, or why you thought it was so important that you almost cried while saying it. When it's finally let out, it's misunderstood or ignored. It's out there for everyone to judge. It's not yours anymore. And if your secrets aren't yours anymore, then what is?
That's when you purposely lock every secret and every detail about yourself inside. That's when you decide never to reveal anything about your self again. No matter how much it kills you inside. The secrets stay within, and can only escape with help from an understanding ear. But even though you've made those promises to yourself, you'll break them. Without a doubt. And you'll regret it as soon as you open your mouth, but then it's already too late.