Patience
Perseverance, Persistence
noun
The root of your energy. You have to dig deep into your energy, all the way to the origin and source of it, to have enough patience to deal with this dumb kid who's eating away at your not-root energy. It's all you have, and you need to use it.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
これは根気のいる仕事だよな。
This job requires patience, huh?
ほとんどの失ぱいのげんいんは、根気のなさなんだよね。
The reason for failure in most cases is a lack of perseverance.
根気よく日本語の勉強を続けていれば、いつかはペラペラになれるさ。
Keep studying Japanese persistently and you’ll be fluent someday.