Attempts to buy off bad luck by bribery.  Bad luck more memorable than good luck.  Covenants were new device for insuring against bad luck.  Entered into all affairs of primitive life.  Good or bad luck became associated with good or bad spirits.  Good luck viewed as harbinger of calamity.  Intelligent human beings still believe in.  Luck regarded as whimsical reaction of spirit world.  Much called good luck might really be bad.  Term coined to cover inexplicable. 
See also: UB 86:1.