It pauses, or slows to a trickle with major life events (getting married, having children, buying a new home), or can stop completely with the advent of a new hobby (firearms, watches, new girlfriend). Basically, you stop/slow/start based on your current desires/responsibilities and available discretionary income.
I think ^^this^^ is more or less true. I've been rather obscessed fot the last 15 months or so, since I "discovered" premium knives (Damn you ZT 0450!!!

). I had some funds set aside from an old side job, and when it became too difficult to find a baja bug that wasn't beat to crap...well, the first knife I snagged off the Exchange last September was like springing a leak in the damn that held back my discretionary savings. I've been kinda insatiable, wanting to experience everything!
There are still a few blades I want for my collection (a large Inkosi, Hinderer Bowie, Olamic Swish, to name a few), but dang, I'm 3+ deep in each class of my EDC. My collection grew so fast that I've reached the point where I don a vacuous stare wondering what to carry on a given day. I have a couple of nice knives just sitting in their boxes new and unused--why pull them out when I've got other great things to carry?
I think I got the most out of my collection when it consisted of about 6 knives (in addition to a few old beaters) -- 3 ZT's, 2 Spydies, and my 'Zaan. I had all my bases covered and just enough variation to keep it fresh. But I have to admit, I really like stalking the Exchange in persuit of my next awesome knife. Then there's the anticipatory suspense of the mail coming, and the rush of opening the box and pouring over every detail of the new prize!
It's definately been fun, but I'm slowing down due to saturation and dwindling cash in he face of occupational uncertainty. I haven't started selling off yet, but I do understand why guys have stuff coming and going, keeping a limited number at any given time (see my 6 knife comment above).
At the end of the day, I look at it like this: I've probably enjoyed the same "rush" as if I've been slowly gambling the same amount of cash at Vegas or with the local tribes. I'd probably have nothing to show for it then. At least this way I've got something tangible and cool to show for it.