"Is it the blues, or is it depression?" ads and awareness campaigns ask.
I think sometimes you get depression from having HAD the blues (understandable response to stressful or discouraging moments) for way too long.
IMO, what REALLY fuels my depression is whatever PREVENTS me from taking action on fixing what gives me the blues!! This makes total sense to me. Whatever that is, it isn't fully depression either, it's more nuanced than that. I choose to label it "learned fears". Those little twerps spoil everything.