He seems confident but deep down he's quite insecure.

他好像很有信心，实际上却没什么把握。

《牛津词典》

I have so many friends, but deep down, underneath, I have a fear of loneliness.

我有这么多朋友，但是内心深处我还是有一种对孤独的恐惧。

《柯林斯英汉双解大词典》

He suspected that deep down, she admired him for having the gumption to disagree with her.

他认为，她内心深处其实钦佩他有魄力反对自己的意见。

《柯林斯英汉双解大词典》

Alfred tried to sound big, but deep down he was like a child.

VOA: special.2010.09.11

So I haven't done magic, I've given you a really fast way to solve a knapsack problem, but it's still exponential deep down in its heart, in something.

所以我并没有施魔法，我已经告诉了你,一种快速解决背包问题的方法了,但是某些方面它的核心仍然是指数增长的。

麻省理工公开课 - 计算机科学及编程导论课程节选

But of course,nobody here is screaming, from which we can conclude none of us really do believe, fundamentally,deep down,that we're going to die.

但当然现在在场没人在尖叫，那我们得出结论，我们中没有人，从根本上相信自己会死。

耶鲁公开课 - 死亡课程节选

For another, it is debatable how much - deep down - he really wants Massa to be champion.

BBC: Hamilton cannot take title for granted

But, deep down, I knew that it had something to do with Raj and his vodka.

NEWYORKER: Raj, Bohemian

Deep down, though, he insists he's still the same guy he has always been.

WSJ: Goal for Jets' Ryan remains same despite changes