Can someone please tell people that the "just" in that sentence is completely misplaced? There is even a certain amount of condescension in it sometimes, when it comes from someone who does believe, has always believed, and has already achieved a certain goal.
But seriously. Has anyone here ever tried to convince themselves that the earth is flat? Sure, most of the time we're talking about subjective perceptions about oneself - "I can write a novel, I will get that girl". But who is to say that convictions in that regard are any less deeply rooted than convictions about the objective facts of our world?
Sure, when you believe in your goals, that will make them a lot easier to achieve. But it's not like you can make yourself believe anything, on command. In my experience, any attempt at such an abrupt change only results in unsurmountable resistance popping up, straight out of nowhere.
I think that, most of the time, especially when the notion I'm talking about is uttered by a motivational speaker or self-help author, it's nothing but a sales pitch. It's not like those people actually know what they're talking about - it's just an easy sell.
For all of those reasons, I rather believe in gradual, incremental change.