Psychonaut Field Manual PAGE 2

I wouldn't call it 'belief', exactly. Although I guess that's somewhat nitpicky — it's as precise as one word can be, and brevity is cool :D But in my experience, what's needed is not exactly a certainty that it'll work, but a certainty that you should do it (otherwise you're just not putting your all into it), and those don't have to be the same. "If nothing else, that would be just fun/useful for other reasons" more than once took me further than what I believed to be possible at that moment.