Comment by jibolash

Imposer syndrome alert. First, wait till tomorrow, see if you feel the same way. From experience, you're probably just in a mood bad because of some difficult task. If you still feel the same way tomorrow, then my advice will be to just take a more deliberate approach to learning. Nobody holds on to details like "very basic OOP concepts" all the time. If you're in a funk because of an interview screw up, get over it. Interviewing is a job in itself. Take time to prepare (3 months at least) and see if you still feel the same way.