Radical 12, meaning eight or all, is one of 23 of the 214 Kangxi radicals that are composed of 2 strokes. "八" is two bent lines that signal divide. Eight is the single-digit number that can be divided by two the greatest number of times.
Fazzioli, Edoardo (1987). Chinese calligraphy : from pictograph to ideogram : the history of 214 essential Chinese/Japanese characters. calligraphy by Rebecca Hon Ko. New York: Abbeville Press. ISBN0-89659-774-1.