Sometimes it happens that on first encounter with a concept we are not able to fully grasp it. It remains mysterious until we encounter one single tutorial or lecture or an in-depth course on that topic sometime later.<p>I never quite understood Python decorators until I read <i>How to Design Programs</i> book and understood higher order functions properly. Then while going through <i>Berkeley's CS61A</i> lectures by John DeNero I got them finally.<p>Do you have any such incident in mind where something finally clicked from a talk, tutorial, summer school, course or whatever?<p>The topic can be anything that can be broadly classified under programming or computer science.