高空作业一直是他最大的恐惧来源。

Working at heights has always been one of his biggest bugaboos.

bugaboos 是名词 bugaboo 的复数形式。bugaboo 指"令人恐惧或困扰的事物"，源自法语词根，原意是"妖怪"或"鬼怪"，后来引申为"挥之不去的恐惧"或"长期困扰的问题"。