Mmm. That does remind of the quite nice social interaction some types of collecting gives. For example, a neighbour was a thimble collector so whenever visiting somewhere, we would look for a thimble. It gave us some entertainment as a tourist, like a treasure hunt, and then the nice moment to give it to the neighbour and show we were thinking of them while away.
It can go wrong though. I've known a few friends who have become associated with "a thing" because their family saw they owned one of "the thing" and now it's the exclusive theme of all presents but they don't have the heart to correct them and reveal all their presents were unwanted!
On the “associated” thing - not so much about collections but there was an interesting article on the guardian website a few months ago, about a woman who came to realise that ‘I like Prosecco’ was not a substitute for a personality, but she had run with it for so long that that was all she ever got as a gift, and she discovered her friends knew very little else about her. A one-dimensional character trap.
As an adult, I go by the motto of “Don’t save the candles”, which is to actually use the things you buy, even the expensive cutlery and the scented candles.
That makes me think that someone who is a hobby cable collector must have the easiest time of it!
People do collect all sort of non-expensive things (pebbles, seashells, ...) so it feels like just a coincidence that collecting pens means also collecting a lot of tools that will never be used.
The Lego I would put in its own category because it was endlessly fascinating and rebuild-able. I used it all the time. The dinosaurs were at least educational.
But the keyrings were just hoarded and gathered dust. I'm trying to decide now if this was unhealthy and trained me to covet stuff, or if it was a good inoculation against the behaviour later in life. I now have zero interest in collecting anything just for the sake of collecting it. I'd rather be minimal where possible, and after accumulating a lot of crap in my early 20s (when owning stuff was a novelty) I now also try to avoid the "I might use that someday" trap.
I too like fountain pens and have about six, moderately priced, all made by 'Cross'. I put various coloured inks in them (I usually have about 3 good to go at any one moment) and ... I virtually never hand write anything.
The thing I have most of is certainly cables and tech widgets of various descriptions, but I don't try to collect them, somehow they just sort-of happen.
Make of that all what you will.