Depression puts a negative spin on everything, including the way you see yourself, the situations you encounter, and your expectations for the future.

But you cant break out of this pessimistic mind frame by just thinking positive. Happy thoughts or wishful thinking wont cut it. Rather, the trick is to replace negative thoughts with more balanced thoughts.
Ways to challenge negative thinking:

Think outside yourself. Ask yourself if youd say what youre thinking about yourself to someone else. If not, stop being so hard on yourself. Think about less harsh statements that offer more realistic descriptions.
Allow yourself to be less than perfect. Many depressed people are perfectionists, holding themselves to impossibly high standards and then beating themselves up when they fail to meet them. Battle this source of self-imposed stress by challenging your negative ways of thinking
Socialize with positive people. Notice how people who always look on the bright side deal with challenges, even minor ones, like not being able to find a parking space. Then consider how you would react in the same situation. Even if you have to pretend, try to adopt their optimism and persistence in the face of difficulty.
Keep a negative thought log." Whenever you experience a negative thought, jot down the thought and what triggered it in a notebook. Review your log when youre in a good mood. Consider if the negativity was truly warranted. Ask yourself if theres another way to view the situation. For example, lets say your boyfriend was short with you and you automatically assumed that the relationship was in trouble. It's possible, though, hes just having a bad day.