I needn't add that if you fail to do as I ask, you will suffer the consequences.

我不必再说了，如果你不能按我说的做，你要承担一切后果。

Or they can fail to do so.

然而他们也很可能做不到这些。

Promise is so beautiful, but often fail to do.

承诺太美，但往往都做不到。

I don't lose heart when I fail to do something.

当我没能做好某件事情的时候，我并不灰心。

The LiveGrid will not work if you fail to do this.

如果没有这样做，LiveGrid将不能工作。