That's too vague.
Let's say I believe I'm too fat. That can make sense if I look in the mirror and see somebody who looks like a sphere. But for an anorexic, when they look in the mirror they see somebody who looks like a stick.
The reason we say they are 'anorexic' isn't because they look like a stick. It's because they look like a stick and think that they are too fat AND they won't change what they believe.
So how do we react to this?
We call something like this a 'disease' and look for something to do to them to make them change. Probably some chemical we can put in a pill or an injection or a patch or a suppository.
Does it really make sense that an inert chemical can cause someone to have a specific idea? Isn't an 'idea' or a 'belief' more complex and specific than a single chemical?
So what can these 'drugs' really do? - other than slow down or speed up thinking?
If that's all they can do, then 'drugging' people just changes their ability to think - their 'thinking environment' - not their beliefs.
So 'drugs' can't 'cure their disease', although they may make it possible for them to think about it differently. Maybe they it makes them think more ssssllloooowwwwwlllllyyyyy. Maybe it makes them stop thinking at all. Or maybe it just makes them passive so we don't have to think about them at all. Or maybe - as my friend who knows these things says - they generally don't work.
But that's not the point.
The point is: if an anorexic didn't believe he/she was fat, she wouldn't be an anorexic. She'd be a skinny person who knew she was too skinny and would do something about it - like eat some more.
So how do you change a belief?
Take football for example. The team which wins consistently believes that they can win. Not only that, they believe they can win this game. Right now. If they think they can't, they always lose.
What makes them believe this?
It's pretty simple: they have a slogan, a mantra, a rallying cry, a whatever to repeat over and over again. So as long as they can keep telling to themselves they can win, they will win, they're going to win - then they believe they can, will and are going to win.
Is a belief anything more than something we keep repeating to ourselves?
What happens when we stop talking to ourselves about one specific belief? Doesn't the alcoholic or a smoker keep reminding himself that he needs a drink or a cigarette? What would happen if he - instead - reminded himself that he needs an ice cream cone? (Besides getting fat and maybe getting diabetes) Wouldn't he eventually go from being an alcoholic to an ice cream-aholic?
A belief is just a thought. It's not made out of stone or steel or even jello. It's 'mind stuff'. There's two kinds of 'mind stuff'. There are memories and there's 'what I'm thinking now'.
All you can do with a memory is either lose it or drag it out to 'think about it now'. Everything you do and experience is the 'what I'm thinking now' stuff. That's where the anorexic and the alcoholic and the smoker 'belief' exists.
There isn't any automated thought loader which pushes thoughts into your 'thinker' and makes you think them. You get to pick and choose.
Don't believe it? Close your eyes and try to count the thoughts which come up over the next 10 seconds.
If you're like I am, there were a lot of them. Ten, a hundred, I don't know. Just lots and lots of them. I'll bet you 'thought about' just a couple - maybe one or two. What happened to the rest of them? They're like the kids you didn't pick to be on your team: they just wandered off.
The stuff you and I believe - about life, goodness, and - especially - ourselves - are just these familiar little thoughts we keep repeating. And by repeating them, we think their real. And that's all a belief is.
So really, how hard is it to change a belief?
It's easy - if you want to and are brave enough to give it up.