RebE > someone carrying in a place where there is no eiruv don’t mention shabbos
say, eruv is down, and you see a mother with a stroller who is not aware of it. You are not supposed to alert her until she gets the kid home safely. Now, in your humros-ness, you say “Hi, whats up” instead of “gut shabbos” immediately alerting the lady (who also learned halokha, of course). As you are probably reluctant to continue exchanging the kid with a lady, not your wife, every arba amos, you would have to find another lady to help, while you will be standing there till the end of shabbos to guard the $1,000 stroller.