Suggesting you can "lead yourself" to depression by simply thinking is just as wrong as suggesting those with real depression can just "snap out of it."
The view that depression has only biological causes is dangerously naive, if not flat out wrong. Depression absolutely can be caused by unhealthy thought patterns.
Of course it did - that's what thoughts are.
This seems like a really strong statement that can't possibly be absolutely true. Isn't there some literature on this?
I remember seeing some "self care twitter" posts with lists of things that "don't cure depression" (thinking happy thoughts, sunshine, Vitamin D) but obviously some of those do send it into remission in many people. Isn't that enough?
It's something that happens over time it's not like a switch.
My answer has been something closer to Buddhist thinking than western religions. It's an intense effort to focus on the current moment. The past is done and cannot be changed. The future will happen, but it's largely beyond our control. It's much more productive and fulfilling to devote all of one's energy and attention to the present. Out of the past, present and future, only the present is real and open to unbiased observation. And practicing removing one's own bias when observing the present moment feels, to me, like the point of life.