Yang attracts yin. Yin repels yin. Yang repels yang. Yin and yang combined in varying proportions produce different phenomena. The attraction and repulsion among phenomena is proportional to the difference of the yin and yang forces.
Nothing is solely yin or solely yang.
Eveything is composed of both tendencies in varying degrees. There is nothing neuter. Either yin or yang is in excess in every occurrence. Large yin attracts small yin. Large yang attracts small yang.