There's a hierarchy, of course, and sometimes the market guides you toward what to sell now vs. not, but basically nothing is bolted. Part of the fun is buying and selling and trading, moving out games you just played a lot for games you haven't, or haven't in a while. You can always (or almost always) re-acquire something you've sold, or sell or trade something you don't like. It's nice meeting people too... maybe a little less so when stairs are involved.