And according to the Threefold Law common in (real world) ceremonial magick, any curse you inflict will affect you at thrice the strength it affects the victim, so perhaps they are correct.
Can it be correct though? If it affects you at thrice the strength in addition to the original effect, isn't 3+1=4 and you end up affected quadruply?
And if you're affected 1x, 3x and 4x... the only amount you can be affected, that they're all equal is zero.