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I did a little research and I found the history behind this quote from Wikipedia:
Keep Calm and Carry On was a poster produced by the British government in 1939 during the beginning of World War II, intended to raise the morale of the British public under the threat of impending invasion. It was little known and never used. The poster was rediscovered in 2000 and has been re-issued by a number of private sector companies, and used as the decorative theme for a range of other products.
P.S. If you're wondering ... we STILL haven't finished our bedroom yet. However, we are getting closer!