The Spear of Destiny is supposed to be the spear that peirced the side of Jesus as he was on the cross. The superstition is that whoever has the spears has the power to control the world ( since it got cosmic godly coolness infused in it when peircing Jesus ), but if you lose the spear, you die instantly.
The superstition has been around...probably since Christianity really took off and many people have looked for it, claimed to have found it, ect.
Do I think it exsists? Yes. I believe there was a Jesus and he was stabbed with a spear, thus making the spear real. As far as the cosmic god juice making it magickal...I don't buy into that so much.