肝心なのは、最後まであきらめないことだ。
The essential thing is not to give up until the end.
He's never around at the crucial moment.
I forgot the most crucial thing.
My phone battery died at the critical moment.
What matters most is not giving up until the end.
肝心 (also read かんじん) means 'essential, crucial' and is unrelated in meaning to 勧進, which refers to temple fundraising; the two are pure homophones.