The messages we receive from other people and from the media are largely negative.
Bad news gets more attention than good news.
If we admire some aspect of ourselves we are seen to be conceited. If we say negative things about ourselves, people will console us. Some people like the attention and sympathy. So they purposely distort the facts and tell others all the troubles and miseries they have. After some time, their sub-conscious mind will start believing what they are saying and start acting accordingly.