"挫折"作名词讲，主要有两种翻译：
frustration（受挫这件事，受挫后的紧张情绪反应）；
setback（使人受到阻碍的事物，挫折；倒退、逆流）。
“只有”的翻译：
only if “只要，只有“，一般表示唯一条件，语气很强，如果用在句首，语序需要倒装；
as/so long as ”只要“，语气比only if 稍弱。
face up to "勇敢面对"
所以这句话翻译的时候，要根据使用什么句式/语境灵活使用。下面分别给出两种翻译：
Setbacks are inevitable in life, for they are a part of life, but they can be overcome only if we face them bravely.
There are moments one suffers frustration in life, and it is just a fraction of life. As long as we face up to frustration, we will be able to overcome it.