The Doublespend Attack is not the same as the 51 Percent Attack

"The double-spend attack is not the same as the 51 percent attack. It is strange to have to make this point in 2020, but it is true: while having 51 percent control of a blockchain makes double-spend attacks free, that is only because it makes ALL economic attacks free. The vulnerabilities are distinct (you don’t even need 51% to pull off double-spending), and fixing the 51 percent attack requires far more than addressing double-spending."

Author here -- impetus for the piece was a few discussions with proof-of-stake people who switched immediately to talking about "finality" (i.e. using validators to prevent chain-reorganizations) in a conversation about economic attacks.

It was actually IMPOSSIBLE to have a conversation about the economic fundamentals of their networks (and vulnerabilities like discouragement attacks) because they kept insisting they they were addressing them with finality. It took much tooth-pulling to get them to see that they were two different problems and they were making no headway on the more difficult one. This is an attempt to condense that red pill into a more digestible form.

Funny thing, I was having a discussion about something related the other day with some folks and the only takeaway I got was that some people either don't understand 51% attacks or pretend they don't.

Interesting read and even more interesting topic. I'd like to know more.