Negative thinking means where people find worst in everything,reduced expectations and have a negative outlook to every situation. It basically depends on person to person and situation to situation that negative thinking causes depression. It depends on criticality of person who has negative thoughts if a person cannot understand the strengths and positive behavior of a person their way of thinking and perception not giving importance and not appreciating to others,try make only yourself superior giving importance to yourself and appreciating your own self for everything in every situation,perceiving that you are the best and can do anything,comparing oneself with others and thinking you can do anthing very perfectly,such people are oveconfident towards themselves, it means, that the person who think negative are having mental illness. It is possible that if parents or any one parent having negative thinking their offspring also has negative thinking. Negative thinking can be relieved only by engaging in a social circle of positive company exchanging each others thoughts, do not think a lot in extremes, do not be in stress all the time, do not involve yourself in a lot tasks, take a break whenever possible, spend more time with your loved one.

Negative thinking is not healthy, although it is not a disease. All you need to do is train yourself to think positive. A life coach or counsellor can help you in this. If you have been exposed to people with unhealthy or negative attitudes then you are more prone to it. But you can choose to change. So seek the help of a counsellor or life skills coach.