How do you prove that something is safe?

Take nuts for instance, we ate nuts fomr pretty much all our history, so it would be reasonable to think they are safe. Yet, in some cases, especially lately, many persons literally risk their life eating them.

So, at most, you can prove something is unsafe, or unsafe in some cases, but you can never really prove something is safe. Life is dangerous, things that are safe for me might be deadly for you. What should we do? Stop any kind of progress because we are scared that it might, somehow, hurt us?

Now, asking that some tests should be conducted before deploying 5G worldwide is reasonable. Asking the impossible, like "prove it's safe" is not.