There was one black female mentee who I noticed was timid in taking credit for her work. I had recently attended a diversity panel where someone in a similar role as me said that in a similar situation, and her advice to her mentee was "Think about what a white man would do" and everyone applaud such an insightful advice. So identifying such an opportunity, I said the exact same thing word for word, basically "I see you're hesitating to take credit for your work. Think about what a white man would do."
Immediately after saying that, I could tell it wasn't taken well, and she asked "what does that mean?" I couldn't come up with an answer for that which wouldn't be taken in a really bad way, so I backpedaled. She later reported me to an administrative person who luckily felt it was too vague to file a serious report about, but told me to watch what I say.
But I do have a solution (my trick). From that point on, I definitely give more subtle advice unless they have passed my test, which is I see how they react to situations where they could give the benefit of the doubt to others in vague situations. Sometimes, I'll bring up a past story about another anonymous person and see if they are outraged and want to get them in trouble. Only the ones who remark that they probably had good intentions, and don't react too strongly, I'll give more candid advice to.
What was wrong with a "be bolder"/"be more assertive"/"don't be afraid of taking credit for your work"?
"Be bolder" is different than "what do you think a bold person would do?"
I have had many conversations with people going through a tough time and unsure of what to do or how to feel in a situation and there is this trick to getting people to think differently that almost always works... ask the question
"What would a reasonable person do in your situation?"
Suddenly the person having trouble coming up with the answer "What should I do?" has a perfect answer to "What would a reasonable person do?"
It's a psychological trick that goes after how one thinks about one's self and how one thinks about someone else being quite different. If you refocus your attention to view yourself from an external objective, you often end up with much better judgement.