I’ll try and field this one, being a person who has been diagnosed with mild/moderate clinical depression, but who isn’t someone with brain chemistry problems.
Probably the best way to describe it is to use a computer metaphor. Let’s say that people are experiencing whatever the computer symptoms of depression are- let’s say blue screens of death.
In people with brain chemistry problems, it’s analogous to having a defective motherboard or memory unit- everything else is working fine, but there’s an actual physical part of the computer that’s not functioning right.
In people without brain chemistry problems, it’s more like a software problem. They’re thinking in ways that lead them to the wrong conclusions about the world around them.
For example (and I’ve used this example plenty), if in your inner dialogue, you use the phrase “should have” a lot, you’re essentially setting yourself up in a way that will cause you to beat yourself up about it. The reason for this is thinking that you “should have” done something, is to think about that thing in a pass or fail way, and to put that item squarely in the failing category.
Examples: Thinking “I should have made a better grade” implies that you failed to make a good grade, while thinking “I’d have liked to have made a better grade” is a subtle difference, but it doesn’t paint it as a pass/fail situation that you failed.
It’s easy enough to accumulate these ways of thinking, and what happened to me is that while things were good they weren’t really a problem, but when things went to hell for me, they became a real issue, because I blamed myself, and saw myself and my responses to these issues as inadequate, and then started viewing my ability to resolve them as incompetent. Which was total bs, BTW, but in my own head, I believed it.
It took my wife to convince me to go to therapy, and then once there, the therapist started CBT therapy with me, and here I am 4 years later, having had some arguably worse things happen than what brought on the depression, and I haven’t had a reoccurrence.
That’s how it may roll with non-brain chemistry type depression. Based on one of my closest friend’s experience, when there are brain chemistry issues, it’s truly an irrational thing- your thoughts are distorted, and you have no idea why, and no amount of CBT is going to change that.
Oh, and Tollhouse, there is a big difference between being down in the dumps or a bit low, and being really depressed. It’s a real difference in the way you perceive the world, and my personal suspicion is that it works like this- something distorts your normal thoughts, and then those distorted thoughts start negatively changing how you perceive the world and your place in it. When you’re down in the dumps. have the ‘blues’ or whatever, you’re temporarily just sad/upset or whatever, and you snap out of it. Depression is something altogether different and more intense.