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i mean he says: he would never put two nickels in bitcoin. He validates this by saying bitcoin is too volatile and only valueable if this small group of people supports it. I think Dave Ramsey would´ve said the same about the internet if he was this age back then. He obviously doesn´t understand the blockchain technology

I am very sure that he has no clue about it. There are actually free courses on Udemy for people to learn on the very topic. Or they can just grab a book from Amazon.

Could you tell me about it in one sentence summary?

He is basically saying is that you shouldn't buy or invest in any cryptocurrency.