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The Good Luck Fairy is the being used by humans to explain the phenomenon of random beneficial events. She1 is derived partly from myth and folklore, and partly from another superstition (mostly of gambler's and card sharks); Lady Luck.
It is the Good Luck Fairy who prevents people from stepping on to doomed aircraft by stealing their passports as they check in, and it is she / he who secretes a banknote into your jacket pocket to be discovered just as you contemplate leaving the pub due to lack of funds. Many people will often wish on the Good Luck Fairy, or even leave her / him a little offering under their pillow before they go to sleep, in the hope that the fairy will grant them some good luck.
However, there is only one Good Luck Fairy, so chances are that if she / he actually gets around to everyone wishing upon them, there will be an influx of good luck which will undoubtedly throw the world into chaos. So, in contrast, it is well known that Gremlins, arguably the Good Luck Fairy's dark-hearted and evil siblings, exist as a horde to keep the status quo.
This 'balance' gives us a valuable insight into the human condition ...
And for more reading on this human condition can we suggest an Edited Entry entitled Luck - an Overview of a Very Human Concept?