“Before you know it” is an English expression that means that something will happen very fast – perhaps faster than expected. It often is used for people doing something, for example “before you know it, he was gone”, “before you know it, she got upset.”

I would like to point out that the grammar of this expression and how it fits with the rest of the sentence is not perfect. For example the proper way to say the first example would probably be “before one could know what was happening, he was gone.” For some American English expressions, however, it is OK if the grammar is not perfect – as a matter of fact, often if you said it the “proper” way, it would not really be an expression anymore.

Some other examples of “before you know it”, if you are talking about how it rained very suddenly when out on the golf course, you could say, “before you know it, it started raining cats and dogs.” Ah ha – like I love to do every now and then, I slipped in another fun expression: “raining cats and dogs,” which means, by the way, that it is raining very hard (I don’t think anyone really knows why it is “cats and dogs” instead of, say “pigs and sheep” …). I better end this paragraph now. Otherwise, “before you know it” I will add another expression :).

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