I knew I should have clarified that. The "Fact" is of course not set in stone. That's the nature of modern science. It's more an approximation.

Like, since the non-existence of an object can't be proven (because it's not observable), it would be inappropriate to for example state "god does not exist". We can't know for sure.

But science works with approximations:

We made 500 different experiments and questioned more than 6 million people from different places around the world. We were able to "disprove" that certain phenomena like lightning strikes can be attributed to a being like god, through observation and analysis of said phenomena. Furthermore, we were unable to find sufficient evidence to support the believe that god exists throughout the entire time we observed and tested events regarding that question. Therefore, we currently believe that there's a 99.9% chance that god doesn't exist.

That's how science works.

If you can prove A but not B, there is a statistical chance that A is true and B is false.

When I said it's a fact, I meant it's a fact that scientists have conducted large studies with many different people during OBEs to assert whether they truly leave their body or not. These tests were inconclusive, saying they didn't prove what these people claimed.

And to quote you: Throughout human history, the sum of human knowledge has always changed. What was a source of fact today, can become tomorrows' generations source of amusement."

Yes, correct. That's exactly what for example the bible is. It was once regarded fact.

Lastly, your teacher uses a famous Japanese proverb: 井の中の蛙大海を知らず (i no naka no kawazu taikai wo shirazu / the frog in the well does not know the big sea)

I'm familiar with it and have heard it many times.

Knowledge can be based on learning or experience. Yes. And while a small group of people claims that their combined knowledge proves something, there's a group a hundred times bigger that says "our experiments say otherwise".

Again, your claim is worthless unless you can measure and prove it. And for that, you need a unified ruler that is the exact same for every person using it, regardless of who they are. That's called objectivity. That's the reason a study has more weight if it had a larger sample size. To remove individual errors.