I went to an interview and now I feel terrible about myself

For real, I totally relate to my mind going blank during interviews... T_T

I completely froze on that question too, but looking back, I realized the interviewer isn’t looking for the right answer—they’re watching how you approach it. So now, when I get flustered, I just say, “Could you give me a moment to think? I’ll gather my thoughts and explain,” and that helps me hold it together. And if the answer comes to you on the way home, it’s often just nerves, so don’t beat yourself up about it.

Well... if you answered all the technical questions, isn't that enough? You can prepare for "the hardest problem you've faced," but it can still trip you up when it actually comes up, and feeling ashamed over just that one thing seems like a bit much. Instead, maybe think about what the interviewer was trying to assess with that question.