Why is it a mistake to over use exclamation points in your writing

Over using Exclamation marks make the writing seem very slang type. if you know what I mean. it's always better to use an exclamation mark after a few sentences (If you decide to only use it in your writing) but not in every sentence. Be careful for such Literature and Language exams. If your making this make practice writing without them otherwise it will cost you marks on such simple mistakes.

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