I suspect that you can relate enjoyment of the hobby to the particular goals and trading habits one sets for themselves.
If you have a highly specialized wantlist and don't stray from it, you may find collecting tedious more frequently. For example, let's say you are an advanced collector of a certain player who has just about everything possible except for a few stragglers you have never seen offered or 1/1s. You may see a new item every once in a while, maybe hope for a new release to feature your player or something like that. Occasionally an oddball item you never knew existed will pop up, but otherwise you are not making much progress on your collection at all. If you branch out in your interests, that may open some new avenues and prolong your enjoyment. If you can't or won't expand your interests, then the hobby is probably a dead end for you.
Personally I have focused interests, but a fairly wide variety of smaller interests. If I had the time and the money, I could always find something I liked/wanted. I collect Steve Garvey, which is a slow and petient process of waiting for new items to show up. However, I also collect Dodger items in general (never ending supply), Dodger autographs (also a potentially never ending supply), signed cards in general, Vintage stars, Topps Rookie Team signed cards, oddball sets and singles and a supply of other players besides Garvey who interest me (Carew, Oliver, Davis, etc). I like SLUs, magazines, minor League sets and the list goes on and on. I don't forsee ever growing tired of the hobby myself, but I like so many different aspects that I have guaranteed my success. About the only thing I don't really care for are unopened boxes/packs and that is mainly my past track record, the gambling aspect (you don't always get your money's worth) and the expense of it.