is this really possible?

simply put, no

there is a limit to what you can do only with your mind. i can spend the rest of my life thinking i can manipulate fire, doesnt mean i will. same there is no way you can develop muscle trough willpower alone it wont work that way. you can convince yourself of things like i dont like i dont like tomatoes or simple things like that but there is no way to change your body at will. if we could everyone would be perfect.

when it comes to your mind it might be possible to convince yourself that you love or hate someone but there is no way that by thinking i want to be a woman your sex will change. your genes wont change because you want it.

But you won't actually believe you can manipulate fire. That's the thing.

There's a fine line between thinking and believing. Unless you were some crazy nut job, you will never BELIEVE that you can manipulate fire. You can think it, but you won't believe, because you KNOW it's impossible.

There have been studies done on this subject, and it may be possible, but there isn't enough proof to support it. Deep down you know whether or not something is possible.