How pens leave and enter the gathering

It’s easy to see how a person who spends years collecting pens ends up owning many of them - even if you only buy a few a year, the numbers begin to add up. For those of us who own under 20 pens, and yet spend time in the hobby, I’m always curious how this happens. For me personally, it’s some combination of restraint, considering exactly what pens I want to add to the gathering, and letting go of pens that do not rhyme with the collection.