What seems like common sense to everybody, doesn't necessarily means it's common sense to someone.
We all perceive things differently and there are alot of factors involved in our thought process. From education and actual life experiences, to just being plain stubborn. But if it's an actual act of deception to intentionally mislead you, or as a prank for humor, you can't always have your guard up. Sometimes it's best to quiet your thoughts for a millisecond and use all that you know and go with your gut feeling.