Comment by quantumgarbage

By "easy" I mean straightforward.

Previous examples which showed how instantiating Fiat Shamir leads to an unsound protocol were so contrived that people use to think that they were a testament to how unlikely breaking FS would be [1].

In "How to Prove False Statements", you can actually build what they show.

[1]: e.g. see https://eprint.iacr.org/1998/011.pdf