JLPT N3. Used occasionally in conversation and writing.
こそ is particle used to emphasize and differentiate. It is appended to nouns and pronouns, very often the pronouns これ and それ and can take the place of the topic or subject particle. The closest direct translation is “that’s just the very thing” as in:
This is just the very thing I’ve been looking for.
That—I have to say—is wrong.
He is the one that is a genius.
The expression is not used with the negative.
[I cannot eat natto]
The particle is easier to understand when used with the からwhere is used to place emphasis on the reason for the second clause.
It was only because I had some I could turn to during that tough period that I’m standing here now speaking to you.
It’s because I have a dream that I don’t mind working late.
That’s all the more reason why you should to discuss with friends.