In the fall of 1973, I fell into a serious depression that lasted for over six months. That depression consumed the greater part of the year I spent working on a Master's degree at McMaster University. In the process, I learned a lot about depression and other things.
Depression can result from a faulty perspective.
My depression was triggered by the break-up of my relationship with a girlfriend. That in itself should not have resulted in depression, but I discovered that, even though I had been a Christian for quite a few years, my life had become focused on my girlfriend rather than on God. I had let my spiritual life slip, and when she departed, it seemed I did not have much left to live for. Since that time, I have learned that it is only in putting God absolutely first that we can receive the grace to really love other people. Depression feeds on itself.