People are not rational. That is what makes us human, I suppose.
One interesting example that's crossed my mind lately: The people we don't like often have more influence over our lives than the people we do.
We avoid locales and social gatherings we'd like to go, if someone we don't want to see might be there. We miss opportunities. All for the people we don't like.
It doesn't make sense. Decide who and what matters in your life, and live it for them. For the people who don't, why factor them into the equation?