Have you ever noticed that people often yell a concerned “careful!” (or the “ooh, careful” variation) right at the moment when the advice is no longer helpful? Try slipping and falling* sometime. At some point after you begin to lose your balance, someone will likely tell you to be careful, as if your fall may not be enough convince you that some extra caution is necessary.
Here’s a typical scenario:
[Thwap!]
Victim: Ouch, that hurt! Too bad there nothing I could have done to prevent it.
Helpful stranger: You should be careful.
Victim: Oh, yes, thank you. I certainly will be very careful the next time I’m WALKING.
* Do not try this