the future is unpredictable; the irony of fate
Proverb derived from a Chinese story; used to express that misfortune may turn into fortune and vice versa, so one should not be overly elated or discouraged by immediate events. Often cited as 人間万事塞翁が馬.
See also: 人間万事塞翁が馬
I failed the exam, but as they say, the future is unpredictable, so this might lead to something good.
I won the lottery, but in the irony of fate, it caused my relationships to deteriorate.