Unfortunately there are many with this mindset. Pull some data for him to read about how depression is a medical illness, brought on by many different things. The science about the connection of the brain's response to our thinking, and the chemicals it dumps because of our thinking is pretty strong currently.

It is common for some to say snap out of it, think happy thoughts.

So while many things can cause us to become depressed, the "cure" IS positive thinking. The brain believes everything we say or think; it has NO opinion of it's own. So if we are not blocking our negative thinking (no one believes me, no one supports me, I can't ..it'll never get better etc) then the brain sends out chemicals to reinforce that thinking. If we force ourselves to rephrase those negative thoughts into more positive ones, countering the negative (well that's not true, that's not always so, of course people support me some just don't understand..) then the brain will dump in the good-for-us chemicals and eventually we WILL feel better and not be depressed.

Quit talking ABOUT depression and why or not you are with them? Talk about how they can help encourage you to think good things and be active...

You felt better in the past...and you will feel good again.