Скажите пару слов на эту тему, можно даже не по-. "if every person swept their own doorstep, the city would soon be clean"

This expression means that everyone should be doing their part and taking personal responsibility for his or her own actions, rather than expecting someone else to get it done for them. It's easy to criticize and complain, it's harder to get things done. Also it means that to accomplish a big project (clean city) one has to start small (sweep their doorstep) and work with others as a team.