Natural olives contain a chemical called oleuropein[0] which has a strong nasty bitter taste that renders them inedible. Soaking olives in a strong brine removes the oleuropein from the olive, turning them into the edible olive people love.

Most people don't know this. It is a common prank to convince people that don't know better to eat the fruit off the tree. As the other poster said, don't do that.

[0] https://en.wikipedia.org/wiki/Oleuropein

I had no idea! Thank you!

Olives are extremely bitter until they’re brined. My wife still can’t handle the brined ones she says it tastes terribly bitter.

This reminds me of lupins which also need quite a bit of preparation before being consumable.

I'm always kind of bemused by the "necessity is the mother of invention" aspect that gave us various food preps and conservation methods.