[incongruity]

Heck, if an avalanche of correspondence fell on any of us, depressed or not, it may well be overwhelming beyond the point of being able to answer it all!

In any case, I would add that the set of actions that matter and make a difference is not a perfect subset of the actions that feel like they're important. That is to say, you never know when something that seems like a small act on your part can change someone else's day...

So, to that end, though I missed the OP's original post, I'd challenge him or her to simply believe in some purpose – find something every morning that makes it worth interacting with others (and try to do so in a generous way) and you're likely to make a real impact, even if you're never aware of it.