What kind of spell are you doing? As Star said, if it's any fluff related spell, it will not work. If it is not something like so, then consider this: if the spell has ingrediants, do you have them? Do you follow the moon phases regularly and the spell requires you to do it on a phase and you are not? Is proper intent being put into the spell, are you saying to yourself that it will work and your mind is not believing so? Look to yourself to see if there is any problems that may arise when doing your spell.