DOMINANT SPECIES

POSITIVE + POSITIVE = POSITIVE

~when one good man meet another good man. they'll be good men.  ( 1+1=2 / 2+2=4 )

NEGATIVE + NEGATIVE = NEGATIVE

~when one bad guy meet another bad guy. they'll be bad guys 

[-1+(-1)=-2 / -2+(-2)=-4 ]

POSITIVE + NEGATIVE = POSITIVE/NEGATIVE

~but, when one good man meet a bad guy. it depends. the results may be vary. [ 1+(-1)=0 / 1+(-2)=-1 / 2+(-1)=1 ]

In conclusion, be a dominant positive-thinker, because dominant one wins a lot.