这可能是个难以启齿的话题。

It can be a difficult subject to talk about.

但是面对我太太，我真的难以启齿。

However, I found it rather difficult to tell my wife about it.

她难以启齿告诉父亲她失败了。

She was ashamed to tell her father that she had failed.

通常那些难以启齿的，不好说出口的，才是最重要的。

Things that are hard to say are usually the most important.