I have had several games that I would "never" sell.
I kept both of them for 10 years and really loved them.
Other games ( most of the ones I have now) I am upside down on and will take a loss on. I will have to sell them for less than I have into them. This makes them stay longer than games I can break even on.
But, eventually the need for space, the desire to get some other game, and the fact that they all get old ( game play wise) sooner or later, has me now not saying "never" about anything in my collection.
You can almost always get a game title that you have had before, so selling is not so final. However, I remember reading a post where someone said " you can never sell your game for what it is worth, and you can never buy that title back for what you sold your copy for." I do believe this to be true.