不是无坚不摧的城墙没有百毒不侵的心脏
[bù shì wú jiān bù cuī de chéng qiáng méi yŏu băi dú bù qīn de xīn zàng]
This nickname expresses the vulnerability hidden beneath a seemingly impregnable exterior. It means someone has strong protection but also admits their own weakness and susceptibility to emotions.