You probably grew up brushing your teeth with modern toothpaste, and had fluoride in the water.
This isn’t universally true, even today, in the United States. So says the diner in Indianapolis I went to where almost all the staff were missing teeth.
It’s something like the second law of Thermodynamics. It’s probability, not absolute. It’s possible all the gas molecules in the room arrange themselves one corner, but it’s fantastically unlikely. It’s possible to choose the right encryption key to a 256-bit cipher at random the first time, but it’s fantastically unlikely.