I wouldn't believe it either unless I heard it directly from my earnest friend who learned at that moment:
1) cars have oil
2) said oil should be changed regularly
1) cars have oil
2) said oil should be changed regularly
Similar to how this person went most of a lifetime without noticing and wondering what oil change businesses, advertisements, coupons, etc were for... They also didn't notice someone in their household or a service provider of some kind (brakes, tires, idk) changing their oil.