You fail to recognize that it matters not what someone is born, but what they grow to be.这里面的you are to recognize是主谓宾，that和but引导的并列宾补，我理解的对？what 在句中做什么成分为什么not可以否定它?
【答】You fail to recognize 是主语和谓语动词， that it matters not what someone is born, but what they grow to be是宾语从句；在这个宾语从句中， it 是形式主语，matters 是谓语动词， not what someone is born, but what they grow to be 是两个主语从句，由 not ..., but ...连接。前一个 what 是状语, 后一个 what 是表语。
