I have multiple projects going at the same time.
If it is something that I want to concentrate on, and not risk being interrupted, I knit at night after the kids are in bed and while DH is watching TV in the living room.
If I think I might get distracted -- like in a waiting room or something -- I have a blanket that I won't lose my place on.
However, knitting is not my primary hobby and one reason I do it is to have something to do with my hands when I'm otherwise stuck sitting in one place for a while. I haven't tried anything that has a complicated pattern.