Suspension of disbelief...okay, you're in the past, you will not want to attraction attention to yourself for fear of being locked up in a psychiatric hospital. Fast forward to the future, no one will believe you because they'll think that you had just read a history book or an old magazine and are making things up..hence, also a lunatic. Therefore, people who come from a different time could be living among us and we'd not know it.
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vapir oxygen