You can loss in demo account and you can learn like what is to make loss even in fact you don't lose anything but it will struck you especially if you are still a newbie. In this case you will learn also how to manage your emotion well without affected so much even not as big as what will struck you in real account later but demo account gives you the overall picture.
Demo account must be maximized by trader as well as possible. And yes, we will get loss in demo, but from this experiences, we must try to be better trader. It's the key to use to get maximal result in forex