In general, clever tech details are probably the things that surprised me the most.
A really ridiculous example is that the whitepaper - and v0.1.0! - got the basic consensus algorithm fundamentally wrong. Satoshi originally thought chain selection should pick the chain with the most blocks. But that's completely busted, as that chain doesn't necessarily have the most work. So Satoshi had to actually change that to the current most work rule, after v0.1.0 was released!
To this day this mistake still causes problems when academics read the whitepaper and don't realize that it's incorrect.
I always assumed that was misstated rather than an outright error. TIL!
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Is the consensus "chain with most work" or "longest chain with most work", if they are not mutually exclusive.
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The former.
Notably, this means that in certain hypothetical circumstances a node can reorg to a shorter chain, with more total work.
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