There are so many great pipes and pipe makers. I have told myself many times that a particular pipe acquisition would be my last, because I would have everything I could reasonably want. But my tastes evolve and I may fall in love with a particular shape, or I may find a pipe maker whose work really grabs me and I'll want to have a few more of their pipes. It happened over and over again. Also, my approach to "collecting" was really to buy pipes that appeal to me and to have a range of different pipes that would cover my tastes and allow me a suitable pipe to fit any mood or occasion - this probably leads to more pipes than if you collected one particular type or brand.
But, for me, there came a point where space to store the pipes became an issue. And I look through my pipe agglomeration and I have at least a few of every style of pipe that I would like. There's also a level of guilt that built up when I see some of the great pipes I have and realise that I don't smoke them as much as they deserve - just because I have too many. In short, approximately 200 pipes is the stopping point for me.
I still look at retailer websites and I see pipes that I like, but I don't have the same compulsion to buy them any more. I've always got something similar already which I like just as much. I also only really look at pipes from two or three pipe makers now, and I have no more interest in what other pipe makers are making - that could only lead to unnecessary purchases or (worse) a further commitment to buy a few more if I really like them. I just decided what tribe I am in and I'm happy with that, if you see what I mean. For me, now, Roush, Le Nuvole, Asteriou, Parks and Former are the only pipes I have interest in looking at, and I probably have enough of all of those already.
If I do see a pipe that tempts me I don't buy it right away, and I wait and see how I still feel about it a week or two later. If it has sold, well there are many more great pipes and you could always commission what you want, but I generally accept it as a good thing that the temptation has been removed and I can put the pipe out of my mind and light up one that I already have instead. Almost all of the time I decide anyway that the pipe is not something I really need in my collection. Other times I feel that I would like it but not enough to justify the cost, given what I have already.
There is an end. At least for me.