chink in someone's armour idiom
（某人性格或论点中的）弱点，缺陷，薄弱环节
a fault in someone's character or an argument that may cause problems for them
A single chink in our armour at the negotiating table means we could lose out badly. 在谈判桌上的任何一点漏洞都意味着我们可能会惨败。