like a shark

It may be a hard act to follow that a foreigner strives to have English as good as highly educated native. Today in a meeting, I was the only one at sea when someone mentioned "Wow, you are like a shark". After googling for a while, it dawned on me that since sharks always swim and never sleep, "like a shark" is a metaphor of "always going forward without losing any momentum". It is almost a weekly routine to encounter this kind of phrases that do not exist in any dictionary.