they are only true if you believe in them, if you are trying to cast one, and you doubt that it is real and you think it wont work, then of course it wont work. you need to have belief! and that's the all the truth I can give you, cause the rest is up to you to decide. do you believe?
I agree while most are real, there are some that are fake, also look at the ratings on the spells here on SoM, the ratings will tell you which ones will work, and which ones wont or are most likely fake.