I don't think anyone can know and prove for definite that depression is a mental illness due to a chemical imbalance. That is one perspective that people choose to follow without getting to the real underlying issues related to their depression.. Regardless of what circumstances we have, or what life throws at us, its always up to the individual how they percieve and respond/deal with things and that has effects. People have different beliefs, and deal with things differently that have different outcomes. Your view of not being able to recover, overcome depression, that is gonna remain for rest of your life cos your brain is not working properly,normally like others, doesn't come from you personally. People have influenced you to think that and you've followed it. You don't know /cant envisage how you will be in the long term future, that you will always be depressed forever.