I do tend to agree with Wendy. I think normal does exist, and is just a word for how the majority of people are and should be.
I think it does help to believe in normal. It helps you to recognise when you're ill. If you're crying every day, can't get out of bed, if you scream at your family, if you want to die..... once you realise it's not normal, you can sort of realise that you don't HAVE to be that way, and seek help.

I was told by someone once that "it doesn't matter if you don't eat that much, you look great. and i often go a whole day without eating".... I took that to mean that I wasn't ill (I was younger then), and I thought well if he doesn't eat either then I'm not sick am I (I was anorexic). But now I can realise that he didn't eat because he was lazy or not hungry, but I didn't eat because although I was extremely thin, I was obessed with losing weight, and THAT's not normal. I think that's when normal is important - I realised that starving myself wasn't normal, that it meant I was ill, and that I deserved to get help.