Though I've never had depression, I have had friends/family/significant others who have had it. I've learned A LOT about it from my current BF who was on Lexapro and my mother who was also on Lexapro. My boyfriend got help the "right" way... he went to a counselor and groups for talk therapy while taking his meds. As people in previous posts have stated, depression is caused by a chemical imbalance. This imbalance is caused by your own frame of mind though. If you are constantly in a sad, apathetic mood, your brain thinks that's how it's supposed to adjust, and causes the imbalance of important mood-regulating chemicals (Roughly the same thing with soldiers who have killed people, at first it's traumatic, but they "get used to it" and thier brain doesn't release the same chemicals that cause remorse. Also seen in sociopaths, etc). If you take the meds without talk therapy of some sort, you're going to be stuck in that same frame of mind... Lexapro isn't magic; in fact it gave my BF bipolar disorder before it was caught and the type/dosage was corrected. By getting counseling at the same time, it helps retrain your thought processes to make the correct insinuations about how you are supposed to feel about something. My bf decided for himself, that he wanted to stop Lexapro on his own. He still went to therapy for 4 months, but he said he learned how to deal with his emotions correctly and could do it without Lexapro.
In contrast, I hate to throw my mom out there but I believe it's a good example on how to not overcome depression. My mom was also on Lexapro, but she went to counseling for about a month and grew tired of it. She is retired, and sits at home on her laptop pretty much all day, never got dressed, no human interaction. So she had tons of time to sit and brood about her feelings. I'm pretty sure she became bipolar also, because when I come home from college, she can be super nice, but then turn in an instant and be super mean. A few months ago she also decided to stop taking Lexapro. She claims she feels better, which is her trying to be in the correct state of mind, but I can see she still has depression and it kills me that she wont admit that she still needs counseling.
tl;dr: Any mental disorder caused by environment (traumatic events, lifestyle) can be corrected with talk therapy (Except schizophrenia). Meds "help", but they are just training wheels in the process to getting your brain back on track.
So! Hope that gave you some insight. /steps off soap box