My take on this
By showing, not telling.
You want to show their actions, not talk about them as a narrator. They need to discover the character’s traits themselves rather than have them being told.
For example saying Samantha is adventurous because she does this or that, bla bla bla is boring but showing that she’s a mountain climber, travels to jungles, looks for idols, and does all sorts of crazy stunts shows that she is adventurous.
Same for a smart character-rather than saying they’re super smart, just show that they gets good grades by doing all of their homework on time, and other school approved actions.
So, yeah, too much exposition is never a good thing.
You want to aim to show your readers the character’s personality, not spill everything about the character to them in a small text box.
Readers want to get to know the character better and go on their journey : )
So, to sum it all up, when it comes to talking about the personality of characters rather than showing their actions & emotions, you want to avoid doing that. I guess a little explanation is good, just not TOO much.
Thank you for reading ^^