... 结构中，不定式表示的“否定意味”。
too + 形容词/副词 to do：由于too 表达的程度，已经超过了极限，所以导致不定式的动作无法实现。意思是“太……以致于不能……”
如：It is too late to go now现在太迟了，不能去了。
反义问句（tag question）只对谓语动词进行相反的提问，而不管其他成分。
鉴于这个理由，这类句子的反义问句应该是否定形式：
It is too late to go now， isn't it?
It’s too cold to go swimming today， isn't it?
He is too shy to speak to her，isn't he?
It’s too cheap to be good， isn't it?
He is too busy to see you now， isn't he?
He is too young to know right from wrong， isn't he?
