>> Ask you that same question in a different way and you have no idea. Never heard of it. This is why whiteboard interviews are hard – questions that you know, but out of context

In my experience this is true. I "test" my friends on these and most of them always screw up an answer to the questions I asked them just a couple of days ago when the question is slightly different but the underlying principle is the same. This is also why I spend hours on a question I get an answer to easily. Because it's important to understand the principle rather than getting the right answer. You can also conduct this test. The simplest and the most basic test is to ask someone what "binary search" is. Obviously, every developer knows what it is but when you ask them to apply binary search in a slightly different context(pick up any medium binary search question on Leetcode, Hackerrank etc) they will fudge it up. I get the hate "trivia" algo interview questions get on HN. However, I just love them because I have always loved "puzzles"