I guess it's hard for a non-Christian language to translate 'blessing'. There's an element of intent about it - it's more than good luck, it's good luck given to you as a reward.
Beware of my intuitions though - I came from a family where such things were so commonplace that unused crockery at the end of a meal, saving on the washing up, were called 'blessings': 'Clear the table, but leave the blessings'. I think this was just a family thing.
On the other, godless, hand, 'blessing in disguise' often refers to something apparently unfortunate that is probably for the best: His death was a blessing in disguise - it's better for everyone, and he was only suffering more and more.
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