I think its about how nobody ever tells him the truth, all adults said what was convenient to them, and he likes everyone who is honest with him even if they come as disrespectful (as the knight commander and her ex brother). I don't think it was such a good speech either but its his weak point somehow
hmm perhaps beware of the villainess goes this way a bit? she despises the prince though lol, but I don't think I've read anything like that. beware of the brothers also shows hari as a friend for the prince if I remember correctly, but the ML aint a commoner either lol normally the ML is also a noble or archmage, even if not the prince

Lol, I don't see the charm of what she said was so powerful that got the prince falling for her