Quote - KobaltKween says the truth. Using my camera metaphor, if you take an under-exposed photograph into your image-manipulation software, there's only so much you'll be able to correct: over-exposed or under-exposed, information will have been lost.

That's a good metaphor but not compeltely accurate. While it's true an underexposed image can have major problems when it's being brought to the correct exposer, it never loses information if you're talking about DSLR images. It may look ugly but you'll always have the details there once it's brought up unlike an overexposed image. Once it's overexposed to white with blown highlights, you can never have those details back.