You have all the data on the loan and the rest in my first message, so there's no need to imagine scenarios just to say that it's hyper-dangerous and just to write a message. If he had borrowed 50,000 euros in 2017 over 5 years, he would have earned several hundred thousand euros after tax, and that's a fact.
There's no one will be stupid if they talk about the past, you only reviewing what happen in the previous year and say this or that. But, if you're the one who try to do that now, you're high likely scared because no one can know the future.
Yeah I do trust Bitcoin and know Bitcoin price will not disappoint us after holding for 4 years, but as always, we never know about the future.
My mindset, I would rather lost all of my wealth and start from zero instead of in debt and always getting pressure in the rest of my life.