Depression is a state of unhealthy mind and negative thoughts. Personally I have experienced it and I know it may be easy or hard to overcome depending on the intensity and cause of depression.
I had deficiency of Vitamin B12 ("pernicious anemia") and deficiency of sun-shine Vitamin D. Both deficiencies may result to depression. So please get yourself a medical test for both these Vitamins.
Also, if you are working in a tough, demanding or toxic work environment or studying for competitive exams and you could not cope with it, that might be also reason for depression. This might result in feeling of negativity / hopelessness.
Following a daily routine is a must. One needs to go for morning walks, practice deep breathing, pick a hobby, learn to practice daily meditation and join positive support groups nearby who will help you get out of your depression. A depressed person can take external help and come to a point where he is able to help himself and manage his thoughts. In extreme cases you might need to consult a doctor and take medication but this alone won't help. It is just for support.
Fighting depression may seem to be a daunting task because people doesn't understand the underlying root cause for depression which may result in delay in curing depression. But once the root cause is identified and you work towards the cure, success is not far away.
Patience, Faith and perseverance is a must to overcome depression and I am sure it can be overcome with consistent efforts in positive direction.