I don't think you are too hard by putting him in the corner. And I truly think they do understand or make the link between their actions and our reactions.

I have a 10 months old here, cries to put himself to sleep. Not a joke, he doesn't want to be picked up. He just cries to put himself to sleep. Really annoying, but parents seem to find this normal, they are even the ones who informed me of this behaviour.

I got bored of this after ...hummmm... a week! hahaha! So everytime he cries himslef to sleep, I take him and cuddle him like a newborn (with a blanket around him). He hates it. As soon as he stops crying, I put him down and after 1 month he stopped crying himself too sleep!

You are not hurting the child, you are just responding to his screaming! Make sure you do it EVERY time he screams though, so he understands that "I scream I go in the corner"