The big, important puzzle for you is whether you are, in fact, the waste of skin you feel like at the moment. Since wondering such a thing, as painful as it is, proves that you are still capable of self-awareness and reflection, my vote is no. Since I don't actually get a vote on your opinion of yourself, I'll move on to your second, much smaller puzzle -.which is why should you believe the platitude that you have had, and could continue to have, a positive effect on someone else?
The posters before me put their fingers right on the most obvious way ordinary people can rescue ordinary people from a day so dreadful that they want to quit a job they need badly. Have you ever talked on the phone to a customer service rep and heard their voice change from forced cheery courtesy (with an undercurrent of emotionally bracing for more abuse for the millionth time today) to genuine warmth and relief as you make it clear that you not only do not blame them personally for the cable fixer not showing up but understand that they want to be part of the solution? If not, go ahead and behave that way the next time you talk to a customer service rep, or a fast food cashier at rush hour, and keep doing it until you hear that warmth and relief from one of them. It's a beautiful sound, almost as good as having Angel Second-Class Clarence by your side.
Btw, I like to think I have a positive effect on rude obnoxious service reps by civilly but firmly letting them know that crap won't fly. Does 'em a world of good, I say to myself. A positive effect on an unsympathetic group who are in danger of becoming, um, wastes of skin.
Obviously, there are ways to make an enormous positive difference, like Jimmy Carter or Dolly Parton or Malala Yousafzai. And there are ways to try your damnedest to make a positive difference in a big way that may not (yet) make the big difference you are aiming for (that counts - Go Greta Thunberg). But little things that might mean a LOT to someone else? You probably do those every day, and if you don't you can start any time you feel like it.
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