Look around and see there are some people who can only see the negative aspect of things and they will have always complaints to make about their life and others.
Then, why do they develop such kind of an attitude? I fee, lack of fulfillment in life and about the things they have done. They feel sorry for themselves, so tend to push it on to others rather than taking responsibility for what they are, for it takes so much of courage to accept that they have done mistake and they need to correct. Rather it is very easy to accuse others for you mistakes and blame them for your wrong way of doing things or your negative attitude.
However, it is such a painful experience to live with such people. When we can think positively and see the good in the other it so wonderful to live together. However, we also need to distinguish the situation wherein we need to make some complaints for the sake of the whole society and the others.