We know for a fact - it is absolutely proven - that swimming in the ocean is dangerous. It can be LETHAL. People die every year from drownings, boating/skiing accidents, and the ocasional shark attack. Dozens die in the US alone, every year, not to mention the thousands of injuries of all kinds, from lost limbs to jellyfish stings. All completely preventable, if only they refrained from swimming in the ocean.

Yet millions of people still swim in the ocean every year. They let their children swim in the ocean.

WHY would people take the risk, when they KNOW it's not safe?

Because danger is not a binary proposition. There is risk in every single action we take, but that risk is greater for some actions, and less for others. The less the danger, the more willing people are to risk it.

Leaving phones on in an airplane may not have been proven safe, but given the millions of flights since the cell phone era began, and the billions of people who have left their phones on during those flights, not to mention the billions of ground-based phone and tower signals that planes fly through every day, the risk - if it exists at all - is so incredibly miniscule that it's not worth talking about. And it's certainly not worth panicing when someone leaves their phone on during a flight. People are such twits...

Nothing is impossible, but by concentrating on the things that have a microscopic chance of harming you, you waste time, energy, and resources that would be far better spent protecting yourself from things that have a much higher chance of hurting you.