Comment by qingcharles

Generally apps like Fiddler generate their own cert which you load onto the device and accept. My understanding is this allows it intercept and re-write requests. When you do this, apps using cert. pinning will sniff out your "wrong" cert. and stop working.

No, the idea is that the app has the server's public key embedded in them, and they use that to verify that they're connecting only to the server with the corresponding private key.