[误] When the old man on the frontier lost his horse, who could tell it was not a blessing in disguise?

[正] A loss of many turns out to be a gain.

注：直译出的句子很长，有失原文的韵味。而且，英美人没有听过“塞翁失马”的故事，所以他们也未必能懂。还有一些其它的译法：A loss sometimes spells a gain.; Every cloud has a/its silver lining.; Misfortune may be a blessing in disguise.; Nothing so bad, as not to be good for sth.