Evaluating existing work is often MUCH harder than creation. It often 'feels' easier because most people do a terrible job and offer little more than their opinions. Some intuition: have you ever eaten something you really disliked but you were able to tell that its actually very good because you understood that not all tastes match yours and you can evaluate the various techniques and elements that went into creating the dish? Perhaps more relatable intuition: finding bugs and flaws in a large code base is much hard than writing the code to start with.