Hi, Snick.
Something I feel that a person who DOESN'T suffer from depression should know is that it's not the sufferers’ fault that he or she is depressed. It's not something that they can just 'snap out of'. They should also know that they need support during their struggle more than ever. Also that they should not FORCE the person to do things they honestly don't want to do - merely encourage it.
And for the depressed person themselves... I feel that they should be aware that the people they are close to are also affected by their illness, and that the depressed person is not the only one that has to learn to cope with it. They should never use their depression as an excuse as to why that can't do something... even though the depression may well affect their WILLINGNESS or MOTIVATION to do something.
Well, that's just my opinion. Others might disagree of course!

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Take care!
Ashlee