I think a lot depends on the core causes for an individual.

A combat veteran who was happy and healthy his whole life before he deployed and then experiences severe traumatic stress in combat and then comes home and develops depression has different core causes than I do.

A person who in childhood was abused, neglected, abandoned, didn't get their emotional needs met has different causes than a combat vet. The combat vet may have very high self worth and self confidence and the person who's development was effected as a child may have very poor self worth and self confidence.

Someone with a family history and is strongly predisposed genetically and biologically is another case.

In all three cases there may be structural and functional abnormalities in the brain that need to be corrected. As wolfgaze said things are very fluid. The workings of the brain and mind are changing all the time. Techniques that work in bettering the functioning of my mind may not work for you. And visa versa. Medication may or may not play a role in it. Finding what works is what is important. Consistently applying all the techniques that have been proven to help. Throw the whole book at it and keep trying. Things are fluid and ever changing.

What do you think the core causes of your depression are? Identifying core causes may effect how best to treat it. For example I am not going to do trauma therapy but I do go to therapy. Low self worst and thinking of yourself as a failure all the time might mean focusing on changing your belief system and value structure with self help books or a therapist or a good support network or all three preferably.