I have it on good information from an experienced Ryanair FO who conducts interviews, that the majority of failures occur right there.
He asked a group of us to guess what the failure reason was, and surprisingly nobody guessed it right. Apparently its "accidental arrogance" where in an attempt to appear confident candidates are coming across like they're God's gift to aviation - his words.
Im not saying you did this but it may prove valuable advice if you plan on having a second shot. Quite how you are supposed to balance confident and arrogance is a bit of a grey area made even greyer by how nervous most first timers are. I sympathise with you entirely on this one but things are picking up slowly within the industry.