It must be difficult for those without mental health issues to understand just what it is like for those living with them, so I'm going to try to explain it...
Hold out your hand. Now imagine there is a 6 inch nail directly through the middle of your palm.
You can see both ends of it and it looks and feels extremely painful. It's been there for as long as you can remember, in fact you don't really know how it got there.
More than anything in the world you want to pull it out. But you don't know how to. You ask yourself how can you not know how to pull it out, it's right there for goodness sake, but you have no answer. You call yourself an idiot for being too stupid to not know how to take the nail out.
Other people tell you to pull out the nail. You tell them that you can't. They don't understand what you mean, just do it they say. You can't, you try to explain, you don't know why you can't explain, they get confused, you both get angry.
The nail is affecting everything else in your life. You muddle through and do things because you have to. The pain gets worse. You start not doing things because that means the pain doesn't hurt so bad, but it's still there.
Soon you are doing nothing.
But the nail is still there. So is the pain. You focus on the nail, you hate it. Nothing else gets a look in but the nail. People close to you start to back off because you are fixated on this nail. They still wonder why you just can't pull it out.
The nail starts to infect the rest of your body. Other things are sore because of it. You forget about them because the nail is the cause and you think that if you can remove it then everything else will be fixed. You still can't remove it. Everything else gets worse.
There's just you and the nail now. Nothing or no one else matters. They're still there, you can see and hear them but they don't understand that you must concentrate on this nail otherwise you'll never be able to get it out.
Something distracts you from the nail for a few minutes. You hide the hand with the nail in it behind your back. No one else sees it, you look like a normal person. But the nail is still hurting. You want to stay with the normal people, you are having fun talking to them, people like you.
But the pain from this damn nail is getting worse. You excuse yourself. Maybe if you just have some time alone you'll be able to pull the nail out. It's just there after all, it's simple, just pull it out.
You can't.