Einstein is disagreeing with that: he's saying that people who are dishonest when it "doesn't really matter" cannot be trusted to be honest when it does matter. (So there are no cases in which dishonesty doesn't really matter.) People who cheat on homework are apt to cheat on exams. A journalist who plagiarizes on minor stories may completely fabricate entire sources and facts on big stories. A teenager who steals $5 from his mother's purse may become a young man who embezzles from his job.