[7777fps]

If you can hash faster than everyone else combined you can re-write history. So you could make a transaction and then re-write that transaction out of history allowing you to spend that money again.

When you make a valid transaction, you have the necessary details for both that valid transaction and no transaction at all. Just because you can't make invalid transactions doesn't mean you can't effectively steal.

This is why lightning network is a shitshow, because you have to be constantly alert for that behaviour.

[pat2man]

It’s an eventually consistent system, so you can defraud people who don’t take that into account. But internally it will always be consistent.

[7777fps]

And by "don't take that into account" you mean "transact anything off chain" including other currencies, goods, services, etc.

[pat2man]

You can transact off chain. You just have to calculate the likelihood that your transaction will go through, and adjust accordingly. The cost of a 51% attack for 24 hours is a lot higher than the cost for one hour, so if you want for 24 hours the likelihood goes way up.