Is that "reason why ... is because ..." right or be common used?
In my country, teachers teach us students grammar, and say "according to the Grammar", it is not right. But in movies I've been seeing many times that the native speakers used "reason why ... is because ...", so I'm confused.

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Native speakers don't worry about grammar. There's book speak and real conversation. Natives don't care about using bad grammar.

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"The reason is because" and "the reason is that" and the reason is" are all used in everyday speech, at least in the US.