I've owned a lot of cues in the last ten years. I have been accused of being a flipper by some and I would imagine that there are people who would think I was some kind of trunk salesman, but that's never been my intent at all. I've picked up a few great deals that I could make a little money on (and a few dogs, as well!), but I always just reinvested whatever I made back into more cues.
When I was a kid, I wanted a Palmer in the worst way, but never could afford one. When I started collecting a few years ago, my idea was to try every different cue I could get my hands on, to see what I really want to play with. I also used many of these cues for comparison to see what styles I like in woods, wraps, inlays, etc. I've played with weight and balance until I know what works for me. I've played with LD shafts, thin shafts, fat shafts, and every different ferrule and tip combination imaginable.
I've had the pleasure of working with several great cuemakers, and I ordered my daily player to my personal specs. I've also bought cues on the secondary market and met some good sellers out there.
It's been a fun ride, as I'm hopelessly obsessive. I've met great people and learned a lot of things over the years that you just can't find in a book. I've really slowed down over the last year or two, as the economy has dried up, but I'm confident that I have found my Holy Grail of cues (I know I've found it because I've been playing with it for the last four years now and haven't had any desire to change my player). I have tested out a number of "back up" cues and have chosen two out of the lot. I will still try an occasional cue, but I've narrowed down my selection features, so I at least know what features I need on a cue from the start.
To answer the OP's initial question, when I found the right mixture of things I want on a cue, combined with the looks, feel, and balance I like, the cue is a keeper. I think I could have made any of the cues I've owned a shooter, but when the "right one" came along, it was as if the cue was an old friend just waiting to find you. It feels like it's a part of you and yet seems like there is nothing really there. You don't seem to notice that it's not connected to your body. All the other cues I've tried were great in their respective way, but were stepping stones to finding Excalibur...
Steve