N3 — outside your level filter
こそ
N and no other — singles its noun out against everything else in play
努力こそが人を変えるのだと思います。
doryoku koso ga hito o kaeru no da to omoimasu.
It's effort, more than anything, that changes a person. neutral
今度こそ絶対に合格してみせる。
kondo koso zettai ni goukaku shite miseru.
This time for sure, I'm going to pass. casual