‘A blessing in disguise’ is commonly heard in both social and professional situations and refers to the idea that something that appears to be a misfortune can have unexpected benefits. A ‘blessing’ is a prayer asking for a gift from the heavens, and a disguise conceals the real identity of something. So, this idiom is something positive which is concealed to look like something negative.
The lady fell over in the street, but it was a blessing in disguise because the man who helped her up turned out to be her future husband.
Losing out on the promotion was a blessing in disguise, because he upskilled and eventually got an even bigger promotion.