I think I understand it now. Basically, it's saying that it's a waste to start thinking about your depression while you're doing something else, say hanging out with friends. Depression is always going to bother you like an ex boyfriend, but getting stuck thinking about depression itself, like "oh, this depression is really bringing me down, why can't it just stop bothering me" is only going to make it worse, so instead, you should put it at the back of your head, try to ignore stop thinking about it even if you can still FEEL it, and then be depressed about being depressed later when you have your good times to remember.
I actually kinda do something like this. I start hating myself over something in a conversation, and then basically just go "you know what, remember that, and then beat yourself up over it later, right now, just try to enjoy the moment". Like, I still want to die, but I'm distracting myself with everything else so I'm not actively thinking about how I want to die. Works shockingly well.