DY and LF: With that premise, we can assume that if someone gives tzedakah, then they are doing it only for themselves if they don’t give also to everyone else who is in need.
If I help one person, I must help anyone who needs to my help, otherwise I am being selfish when I help that one individual.
Likewise, the fact that ZD tries as best he can that nobody gets injured from the snow in front of his house, has nothing to do with being a mentch. In order to really do it for others, he must spend the whole day shoveling the whole city. And why stop in his city. Why not the whole country?