The origin of 六 is still the subject of debate. Some believe that the Oracle Bone form of 六 was a pictogram of a tall mound; believing that a tall mound is something that is beyond the norm, and that the number six is beyond the normal scope of counting to five (for the number of fingers). Some believe that it is an ideogram or ideographic compound meaning: an even number that 入 (Enters) 八 (Eight).
Because it is pronounced similarly to the word 溜 (liù) meaning "Flow", 六 indirectly conveys the meaning of events "flowing smoothly" and is considered lucky, especially for business.