I had so much confidence for this interview but bombed it completely.

I felt so confident and had practiced all week for my interview. I know my shit but then the first question was something I didn't expect and didn't have an answer to. Instead of saying something like "I don't know the answer at the moment but would take the time to research it" or adjacent I tried so hard to sound intelligent and that I knew what I was talking about and fumbled it. I made a face and just said I'm so sorry I'm nervous and my train of thought keeps leaving. The interviewer proceeded to be empathetic and told me that he gets it and that interviews suck but this is a senior position and the nerves made me look like I have zero pitch skills. It was kind of him to say that this didn't determine my candidacy but I'm not stupid and I know that it definitely DOES. I'm so ashamed of myself that my stomach feels queasy from sadness. I work so hard to prove myself and it always feels like there's some silly barrier. I answered all of the questions after that with confidence but why did I have to do so bad on the FIRST question. This is just one of many things that would be used to pick between candidates and I gave a very clear bullet point in their notes about my cons. This job change would've been everything that I needed and I feel like I just watched it fall through my fingers in an instant.