Bumbo asked his teacher, “Do all conjunctions need commas?” The teacher immediately struck him. “Why did you hit me?” Bumbo cried. The teacher answered, “Because.”
The word because is a conjunction. It is a subordinating conjunction, which means it starts a dependent clause. The teacher hits Bumbo to teach him not to put commas in front of all conjunctions, only in front of coordinating conjunctions that join two independent clauses.
He answers because to indicate that a comma before the word because is the most common mistake that writers make with putting commas before conjunctions to join independent clauses. Because is not a coordinating conjunction, so it cannot join two independent clauses and is not preceded by a comma. If you put a comma before because, your reader may “hit” you because that comma is wrong.