First of all, I don't think most mental illnesses can be treated simply by willpower alone. And, in some cases, all the available treatments and remedies we have will sadly not bring that person up to a functional state. I hope this is rare, but I know it is possible.

However, that's not what I think of when I hear that a person must want to change in order to do so. What I think is that one must make a commitment to oneself to go through treatment and try to reach a higher state. Working through such an illness and getting help can be a long and difficult path, and there have been many times when I myself have just given up and let myself succumb to what I saw as the inevitable. But before I could really start making major steps forward in my treatment, I had to acknowledge my problem and decide I was willing to work through it. If I shut myself off to the world, then no talk therapy or anything can work, because I'm not in a place where I'm willing to accept that help.

Thus, I think making that choice to want to change is major. It's not necessarily as easy as people think, and I know sometimes I and others are not in a place where we feel strong enough to make that journey. Sometimes people need to be brought up to a more functional state first before they can start the path to true healing. This is not a reason to judge them, but an element of the illness that needs to be accepted and understood. It doesn't undermine the fact that strength and perseverance of the ill person can be crucial to their own recovery though.