(not) always; (not) necessarily — often used with a negative sentence to mean something is not true in all cases.
高いものが必ずしも良いとは限らない。
Expensive things are not necessarily good.
彼の話は必ずしも事実とは言えない。
His story cannot necessarily be said to be true.
努力すれば必ず報われるとは必ずしも言えないが、無駄にはならない。
You can't always say that effort is always rewarded, but it won't be wasted.