Depression doesn't give a fuck about your successes. Look at Chester Bennington, Chris Cornell, or all of the doctors and lawyers who end their lives each year. Behavioural therapy can do a lot of good to help improve the way you see things and mitigate how low you drop during an episode, but for the most part it seems to be a chemical thing that occasionally just decides to fuck your day/week up. The fun thin about being depressed and successful is that you'll think, "I don't deserve to feel this way. I have it so much better than others," and then your guilt loops back to feed your negativity. Sadness sucks, but depression is a killer.