Vitalik Buterin proposed that the theoretical ideal for digital identity systems is to allow N identities per person at a cost that grows quadratically (N²), thereby preserving pseudonymity while discouraging mass identity farming.

Quotes that support claims

There can't be an easily legible hard limit on how many identities you can easily get. If you can only have one identity, you do not have pseudonymity, and you can be coerced into revealing it... pseudonymity is fragile, and so it requires a large safety buffer.

The theoretical ideal is something in the middle, where you can get N identities at a cost of N².