Although you probably dream of further adding to your collection, I'm guessing you own one, maybe two, cameras, and a modest collection of lenses. But how about tripods?
When first starting out, most photographers balk at lugging around a tripod at all, viewing them as not dissimilar to a ball and chain around their ankle. They're awkward to carry, and more so to use. All those gangly legs to wrestle into position kind of takes the spontaneity out of things. But as they progress in their craft, they increasingly become resigned to owning one to hold their camera still. Like it or not, a tripod is a necessary evil unless you're fond of blurry photos. At this stage, the question becomes one of buying the best tripod they can, or at least one that is good enough to do the job. But rarely do aspiring photographers dream of owning multiple tripods.
But the truth is, just like lenses, no one tripod can cover every need. Big tripods can support a greater load but weigh more and often can't get very low to the ground. Lighter weight tripods are fine for everyday use but aren't sufficient for more demanding applications. Smaller, ground-level tripods are perfect for, well, shooting and ground level and little else. You get the idea.
My general purpose tripod is a carbon fiber series 3 Gitzo Mountaineer with three leg segments. Tripods with four leg segments collapse smaller for more comfortable carrying, but are inherently less stable due to the extra leg joints. And with four leg segments that must be able to nest inside each other, the bottom section ends up being unnervingly skinny. The legs extend longer than I typically need, but I love the fact that it can still reach eye level, even when shooting on a steep hillside. It has no center column, so the only way to achieve height is by extending the legs. And raising a center column decreases stability by turning a tripod into a monopod with three legs underneath, and complicates shooting near the ground. For most shooting, this tripod works well for me.
But if I'm planning to hike very far at all, my main Gitzo can slow me down and make my back and shoulders hurt. It's literally a pain that it weighs so much. When I leave the heavier lenses back in the car, I don't need such a heavy tripod, so I have a lighter weight carbon fiber series 2 Gitzo. I don't use it that often, but it helps lighten the load when the situation fits.
I also have a sturdy old Bogen/Manfrotto tripod that I hate for regular use because of the lever locks. Undo one of these, and the leg goes completely loose and collapses freely into the segment above unless you're holding on. The Gitzo twist locks effectively allow for variable friction. I like being able to partially loosen a joint to make a small adjustment or unscrew further for freer movement. But the Manfrotto works better for shooting in tidepools because it's easier to clean after I finish shooting. I've written before about how to disassemble and clean a Gitzo, and it's no small task. The Manfrotto is simple to clean in the field by undoing all the leg locks and rinsing it with a hose or faucet.
Then there's the whole line of GorillaPod tripods from Joby, of which I have several. Perhaps only one of these would have been sufficient, but they kept coming out with better versions, and I'll admit to eventually justifying upgrading more than once. These things are great for shooting at ground level on uneven terrain. So long as you are careful of weight limits, you can contort a GorillaPod into whatever shape it takes to point your lens in the right direction while allowing for near-zero ground clearance. I've had an obsession with shooting as low as possible, and I love GorillaPods.
But some lenses are heavy enough that they would squash a GorillaPod like a gorilla, perhaps King Kong, if you a more specific metaphor. By inserting a small extension tube between some really big glass and a camera body, you can make an ultra-telephoto that can focus up close. I have an earlier model Nikon 500mm f/4 AF that's big enough I wouldn't dream of hand-holding, but I also wouldn't dream of shooting without some support. So long as the terrain is relatively level, a Platypod Max fits the bill perfectly. If you've never encountered them, Platypods are nothing more than flat metal plates with a mounting screw in the middle of one side that can accept a tripod head. Set it in the middle of a field, and you can get some great wildflower shots with blurred backgrounds due to the shallow depth of field.
I suppose you might be able to get away with a single tripod if you limit yourself to only one type of subject matter and point of view, but why bother? Good tripods may not be cheap, but they can last for many years if well maintained. I have so many tripods in part because I've just had some of them for so long now. Some of them have done duty as support through numerous camera upgrades. By now, I have quite the collection of tripods.
And then there are monopods. I only have a few of those, but we'll save that topic for another day.