What is the origin of 'a blessing in disguise'?

People who believe in gods cannot usually accept that their deity would dump on them. As a consequence any bad turn of events must serve some "higher purpose" which they are incapable of understanding (being "only human")

The term "blessing in disguise" therefore means any bad thing that happens that has to be explained away without blaming a deity (e.g. "Getting cancer was a blessing in disguise as I now don't have to worry about paying for extended coverage on my electronics purchases")