Depression is such a monster, you can't understand unless you have felt it.
It starts as that sad feeling, almost like you're so disappointed in everything, yet nothing at all. Something is missing!
You have a hole which can not be filled and the more you try the emptier it gets.
Depression has no discrimination, it doesn't mind your circumstance, not really. I have been in the most pain of my life physically but been happy. I have seemingly had it all but felt so empty.
That disappointment is almost constant, you feel like you are a disappointment, people either don't notice that you feel so low, in which you feel disappointed you are that insignificant they don't notice or worse they try and cheer you up and when it fails you feel you are a disappointment to them for not being able to cheer up.
You take up a hobby, keep busy, take your mind off it... It's going so well until... you make a mistake, doesn't look quite right though probably fixable but to you that's it, your crap, this is crap every things crap... and again your disappointed.
Sometimes you keep your mind off it and your keeping that hole covered, not filled you know you could fall back in...
I've been in that hole so many times over the years, I scrape at the sides but I set goals I don't hit and BAM feeling low and disappointed...
Don't try and cheer someone who is depressed up... go to them and tell them one thing, just one! that makes you proud to know them.
Lets all stop feeling disappointed...
(Having suffered with depression for many years I know that medically there is chemical imbalances and I hope not to make anyone think I belittle depression as just disappointment... This is my personal relationship with my depression and the best way I can describe the feeling I have. )