i've forgotten the most elementary stuff in interviews.. half the time if someone asks me what object oriented programming is, i can't remember basic tenets (encapsulation, polymorphism) yet i have no problem coding up a dependency graph pattern.

whoever breezes through such technical interview, has either just had 20 interviews with similar questions and it's fresh on their mind, or studied specifically to become good at technical interviewing.. The latter is what i figured out that i had to do to stop being rejected from jobs i was clearly qualified for, just because i couldn't articulate something i never really had to articulate in the past.