我觉得这可能是个笔误，可能是在 just 后面漏了一个连词，比如 as, when之类的。即：

The car must break down just as we were starting our holidays. 我们刚刚开始休假，汽车偏偏坏了。

The car must break down just when we were starting our holidays. 我们刚刚开始休假，汽车偏偏坏了。

类似的例子如：

It started snowing just as we were setting out. 我们正要出发时，天开始下雪了。

I caught him just as he was leaving the building. 他正要离开大楼的时候，我把他截住了。

I could have done without her ringing me up just as I was about to go out.  我刚要出门她来了个讨厌的电话。

Just when she was ready to dip into her savings, Greg hastened to her rescue.  就在她准备动用积蓄时，格雷格赶来救了她的急。

Just when we were all getting our summer clothes out, it turned cold again.  就当我们把所有的夏装都翻出来时，天突然又变冷了。

You start to say something and then just when it’s getting interesting you stop. 你开始讲了起来，可你正说到精彩的时候，却又停了下来。