That "authenticity of host can't be established" message isn't just noise. Here's what's actually happening — and why blindly typing "yes" is a security mistake.

Every developer has seen this:

The authenticity of host 'example.com (203.0.113.1)' can't be established.

ED25519 key fingerprint is SHA256:abc123xyz...

Are you sure you want to continue connecting (yes/no/[fingerprint])?