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》

Deep down I still loved him.

我在内心深处仍然爱着他。

《牛津词典》

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