I've been there several times;
Once I tried to convince myself that one lever action and one revolver in .357mag was all I needed. The temptation to buy other guns/calibers was just too big.
Then I was sure that by limiting my collection to .22, .45 and .308, I would be able to get all I wanted without having too many different calibers. I was perfectly happy with 6 guns in 3 calibers ...
Until I came across a good deal on a MP5 (so I added 9mm to the list).
Everybody at the range seemed to love their SIG550's (so I added 5,56mm to the list).
The possibility to buy cheap surplus ammunition made the acquisition of some Mosins justifiable (so I added 7,62x54R to the list).
Who could resist a nice Martini-Enfield or a jungle carbine (so I added .303 to the list).
Can you say 'no' to a cheap PPSH41 ? I can't ! (so I added 7,62TOK to the list).
I just promised myself that 20 guns and 8 calibers really is my limit and that if I get a new gun/caliber it would have to replace something I already have.
Although ... isn't it a bit silly I don't have a 12-gauge ?