Why is that people that act so “mean” and be “cruel to be kind” care the most?

It seems like the people that are brutally honest, make you feel so bad about what you did or if you’re not taking care of yourself, seems “mean”, says ugly, horrible things (truths) in your face and act “cruel to be kind”. Like some people I know would tell me I’m doing great, but my family or best friends tell me I’m screwing up and I don’t care enough about myself if I don’t take care of myself and rather stuff myself with junk food rather than eating right.” Boy does my family hurt us with the truth BAD.