Depression has many causes, different intensity and duration, it is usually a result of different factors such as genetic predispositions, neurotransmitter imbalance, and also environmental influence such as emotional trauma. So not knowing the exact cause it is difficult to address it.
I found sort of escape from depressions in spirituality. On one side I am quite ambitious and motivated, I achieved fairly good accomplishments in my life, and on the other I always have doubts whether everything - all the ambitions, study and work - is even worth it. These doubts could be perhaps source of depression...
For example, what's the point of studying, building carrier, stressing out at work, investing money, paying bills - if I could be much happier simply enjoying nature? So that's important question, if you start asking such questions you may fall in depression because you will see that there is no point in building materialistic life... There is really not much point of focusing on business, gaining knowledge, saving for retirement, getting girls...
It's all just an illusion that that we as a society live in, it is sort of forced upon us by people and media that we are surrounded with.... We live in illusion that all these materialistic things are somehow important... good car, nice house, good income, social recognition, latest smart phone, pretty GF, sexy wife ... What for? It's all BS, we don't really need these things to be happy...
So if you ask these or similar questions you could get quite depressed. Don't just read those questions, ask them yourself... You won't have much ambitions to get ahead with your life because everything in your mind is pointless. You will just see people around you who are always busy worrying about thousands of useless things, who are always finding importance in some insignificant actions... Have you ever thought of happiness of dung beetles...?
...Thus the spirituality, at least for me. Spirituality removes all the nonsense of this world, it will allow you understand that it doesn't really matter whether you are so called successful or not, because the "success" is really just an opinion of different people who themselves are clueless about this world, about what is important or not...
All the "successful" people are really just seekers of happiness, they think that collecting materialistic things will make them happy... They collect money, they collect success, they collect businesses, they collect knowledge, they collect girls, they collect social recognition, they collect laws, they collect pretty and exotic words... And the more they collect the more they need to collect, the better collectors they want to be... not realizing that all these collections will make them happy, but only temporarily...
That's why all collectors can't give up their collections, they don't know how else to be happy, they don't understand that true happiness starts when you really get rid of all the collections, of all the achievements....
I know, I know, it must sound quite depressing, even confusing. Drck must be unbelievably depressed person, you think. I've never heard so many depressive things on one page, you say, it's fucking depressing just to read about those things.... But that's exactly how collectors think.... The reality is that Drck is quite happy, I'll even bet that I'm the happiest person in this entire forum...
So its not really about intellectual understanding, it's rather emotional understanding, you will feel the pointlessness of this world... You feel with your heart, not with your brain... Feel, don't think... Spirituality will naturally increase your positive feelings multiple folds because those feelings will no longer be bounded to the silliness of this world, to the achievements of diligent collectors, to the happiness of materialistic world... Can dung beetle be really happy when he realizes that all he does is pushing shit against gravity...?
Also, just to make it clear, I'm not for any religion, I avoid any religions, I don't like organized religions... perhaps I don't even believe in God... But the spirituality is big... Spirituality is how you feel, that's how you can "see" through this world, that's how you keep more permanent happiness - because you are no longer dependent on collecting things of this world...