I was just wondering - the Imperius Curse, one of the Darkest curses possible, can be fought, not by everyone, but by some people. So do you think that there are other spells/ potions that can also be "fought"? For example potions which don't so much do something to someone, but affect the way they behave. For example say Amortentia. If someone gave someone else who absolutely despised them Amortentia would the residual hatred be enough for the potion not to work?
Can anyone think of other examples where spells/ potions may not work?