I failed a interview for not remembering the internals of a hashmap. I learned that 20 years ago in university and have honestly never needed to consider it sin

I failed a interview for not remembering the internals of a hashmap. I learned that 20 years ago in university and have honestly never needed to consider it since then. I work with databases, servers and web apps. I was actually surprised at how many of the computer science fundamentals that I did remember after 20 years. While an understanding of how these things work is useful it's mostly unrelated to the job.