Its not a subtle thing that every time you bring another home you start to think "maybe". Its more of a sledge hammer to the side of the head. Its a revelation. When you own too many, you may find rust starting on one you've forgotten about for a long time. Like maybe out in the garage or down in the basement. The guns own you.
Everyone should take an annual inventory of their guns. It forces you to look at them and reoil them. After a couple of those sessions where you decide its time to buy gun oil in the economic 1 gallon size you start to understand.
And about 10 years ago it hit me. I'd been cleaning and oiling guns for a couple of days. So I did the forbidden thing. I counted them! Never do that. First, you need to lie when someone asks. Even if its none of their business, civility may dictate you give them an answer. When you know, you can't say you don't.
Better still, move. When you realize you don't have anywhere near enough gun rugs for the operation, you may have too many (or not enough rugs.) I had to buy more long gun cases when we moved out about 2 years ago.
You may also have to many when you buy a new one and try to make it feel at home by storing it with others of the same type. Then realize you've just bought a duplicate that isn't in nearly as good condition as 3 or 4 just like it. Its when you start packing your bag for the next gun show, putting the less nice 2 or 3 in the bag.
I can honestly say 2 things right now. I have no idea how many I own at the present time, and I've never owned 300 guns at one time. I can also say I don't have anywhere near 300 now. I'm good with that.