Imagine a world in which everyone shouts everything. That's what the internet - and many of our emails and other messages - has become, with its gazillions of exclamation points.
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The reality is that when you add an exclamation point (or more than one!!) to everything, you emphasize nothing. Better to choose your moment to emphasize with an exclamation point; the rest of the time, rely on precise writing.
Here are some appropriate moments to employ the exclamation point: