补充几个特别的：one of those days 倒霉日；one of Those Days 电影名《悲惨一日》。

【例句】
One of those days is none of these days.
莫待他日，此刻即行/择日再约，则遥遥无期。

I think that is one of the major ingredients in his success.
我认为那是他成功的主要因素之一。