I had to think on this for a bit, but its definitely the hunt. When I start a new set, its probably cheaper and definitely easier just to buy the set outright but thats no fun. i usually buy lots of 50-100 cards ( commons) and then hunt down the last remaining few over time. I have been working on some sets for over 10 years. I have been two cards away on one set for over 3 years now, they are out there but not in both the condition and price range I am looking for as of yet, so I continue the hunt. I just did a quick count of my completed sets on my bookshelf, 47, and I cant tell you the last time I looked at them, but I have the satisfaction of knowing they are there and the memories of putting them together