dvcochran
Grandmaster
What about if someone were to say "you're not so good at abc, you can improve by doing xyz"?
That's saying you're not good, but in a constructive way (not destructive, like "hey, that's bad")
It is the lead in that sets up a discussion. When your lead in statement includes the words "you're not good", most people are going to zero in on that making the rest of what you say less effective.