ESK is correct, your believe in the spell is one of the things needed for it to succeed. what is this spell for? certain spells, like transformation, won't work because magic cannot go against nature. be sure before you cast any spell you cast a circle, charge with energy, focus/visualize your intent, ground excess energy, and work to achieve your goal. if you sit around and wait for your spell to work, chances are it won't. if it's a protection or a curse that's one thing, but a love or wealth spell needs to be acted upon.
a spells ingredients don't prove it's successful or not. ingredients aid the spell, but what matters is the caster. if you deeply need it to work, if you charge enough energy, and focus well enough, then it will be a successful spell. if you doubt the spell, or just read out step by step without putting much energy or effort into the spell, then it won't work.