Best size for a collection

[zengineer]

It's like so many other things in life, we often want much more than we need and if we can afford it we indulge.

I think there are two different questions here. To me it's "how many allow me to feel like I'm wearing a really spot on choice every time I'm wearing a watch". Of course we can wear divers with a business suit, but it's really not as good a choice as a Datejust now is it? I have seen collections here of 3-4 watches that cover a wide variety of situations very well.
Most of us would be well served by an Explorer I or Submariner and maybe nothing else. I see collections here that are just a dozen different Submariner and/or GMT's. That doesn't appeal to me for many reasons but it works for that collector. so the second question is more for a "I want them all" collector. They want the black one, the white one, the blue one and the precious metal one because "they really are completely different watches".
I have a dozen or so pool cues and that's 10 or 11 more than anyone needs. I'm sure we all have our "thing we have way too many of". It really comes down to whether you want to have as few as possible or as many as possible.