Why do certain colors complement each other and others clash? Why do certain musical notes complement each other and others clash? Why do certain people complement each other and others clash? It is because all is vibrating energy.
Life is about resonance and dissonance. Your purpose in life is to increase your vibration so that you resonate more fully with the vibration of love. Those with whom you resonate have a complementary vibration to your own. You share similar thoughts and beliefs and radiate a similar vibration of love.
The opposite is true of those with whom you clash. What to do when there is a clash? You can always run away, but this does not raise the vibration of the whole. Love more fully, for all is love. The more fully you love, the more you resonate with all that is.