This is the 4591st most frequent Japanese word.
必ずしも
Not necessarily.
必ずしも is used to express that something does not have to be the case—here it negates the necessity of being a genius.
このクラスで高得点を取るには、必ずしも天才である必要はありません。
To achieve high scores in this class, it is not necessarily required to be a genius.
必ずしも is used to indicate that eating healthfully might not be inherently easy.
健康的な食事をすることは必ずしも簡単ではありません。
Eating a healthy diet is not necessarily easy.
必ずしも is utilized to imply that the truthfulness of his story is not guaranteed or absolute.