Depression is a psychological disorder which does not have a single cause. It is caused by multiple interacting factors. First and foremost is having a fragile and vulnerable self. People who feel shattered and broken emotionally are the ones who are more prone to depression. In depression a person starts to feel weak and horrible about themselves. The second cause of depression is biological. Imbalance in a neurotransmitter called serotonin can also lead to depression. Extreme stress and prolonged stress can also precipitate depression. In anxiety person unnecessarily keeps on worrying. The key to overcome the depression is to think positive and let go all the negative thoughts out of your mind.It's very important to maintain a healthy lifestyle including proper diet and good amount of sleep.