One forgets most of that stuff over years in the industry. They are not difficult to remember either or solve in real time - but it does require practice for achieving consistency. Only having to revise them for an interview is really a waste of time. Let me elaborate with an real life example - programming challenges that require graph traversal and other approaches. If I give one after preparing and revising for few hours over 1-2 days, I can solve all 3-4 questions in an hour. If I revise for one or two hours, I am likely to solve 3, but maybe falter on the 4th. I am the same person in both the cases. Maybe that elaborates the problem and disgruntlement - it pisses me when I pass some and get rejected in another. There is no consistency in the test. :)