Is it correct to say that sufficiency and necessity of a condition is like saying "if and only if"?
My knowing the combination to open this vault is a necessary condition to my finding $1 million inside it.
I will find $1 million inside the vault only if I know the combination.
The presence of $1 million in the middle of the vault that I open every morning is a sufficient condition for my finding it, since it's so conspicuous. I can't miss it.
I will find $1 million there if it is there.