I was watching a video about one of the hardest maths problems even examined in the IMO (International Math Olympiad). And once I was walked through the solution, it seemed so obvious to me, as I'm sure it did for most people. It had a two step solution and was explained very intuitively.
Another example of this is whenever I watch a movie and replay the story line in my head afterwards, it always feels that the story line is predictable. Almost as if I could write it myself. When in essence it's not doubt difficult and I couldn't never predict it's plot line without seeing the entire film.
Given any outcome to an event (such the answer to a mathematical problem or the plot of a movie (or anything really), why do we feel as if it was so obvious?
Besides the throw-away answer of 'cockiness or 'arrogance', is there a physiological phenomenon for this sense of confidence/ know-how one may experience after being told the solution/end to something.