All balances are stored on a shared database called the vault.
When this database is updated, how do you reach consensus on the correct version of the new database?
The only thing you can do is accept the most popular version. But, if someone is conducting a 51% attack,
the most popular version will have an unusually low percent of corroboration, closer to 50%. So the data is only acceptable
while it has a high degree of corroboration - very close to 100%.