Long before it meant a number, 八 pictured an object splitting in two: two strokes curving apart from a single point, like a stick snapped down the middle. That "dividing" meaning was so useful that scribes later fenced it in with a knife, 刀, to build a new character, 分 (fēn), "to divide". 八 itself was borrowed purely for its sound to write the number eight, and the two halves drifting apart are still the whole character today.
A piece of culture
Eight-oh-eight, eight o'clock, eight seconds 八 (bā) sounds close to 发 (fā), "to prosper", making eight the luckiest digit in Chinese numerology — the mirror of the unlucky 四. Beijing scheduled the 2008 Summer Olympics opening ceremony to begin at exactly 8:08:08 p.m. on 8 August 2008, stacking as many eights as the calendar and clock would allow. Phone numbers, car plates and apartment floors with extra 8s routinely fetch a premium at auction, purely for the luck their sound carries.