The one who becomes unhappy in the first instance is the one who is hating. This negative emotion is like a barb which we would like to use to hurt others, but it first pricks the one who is holding on to it. This is a law of nature and so simple that most people overlook it completely. We go through life having a distinct demarcation line: on the right everything we like and on the left everything we dislike. Certain qualities and characteristics are always either good or bad in our opinion. Sometimes it does not work out quite that way and we hate to shift our demarcation line. It's not a comfortable way of living. One is a person who cannot be happy because it's impossible to find only people and things that one likes. Since there is no perfection in existence, there's no hope for happiness in such a mode of reacting. It is amazing that most people have not woken up to this fact. Many have spoken and written about it but it remains a matter of spiritual practice.