It could be worse - you forget you have something and buy it again... It has happened to me a couple times. Two for the Road and Paris When is Sizzles are great examples. I kept getting these two confused and which one I had. So I have two of each now - I think.
When I was actively backing stuff - I would buy a second or third just because they were in poor condition they are price right. I have a extra Superman, Cat on Hot Tin Roof HS, Funny Face OS, two extra Scarface OS, and an extra Mad Max US OS... All still waiting to be restored.
Glad to know I'm not the only one
What I have the most of I think is Star Wars, 3 dated revenge, 4 style A, 3 ESB GWTW... The rest of it, it's just 2 of this, 2 of that, sometimes 3, like Once Upon a Time... I don't want to have doubles and triples, but if the price is right... I see a lot of folks at Emovie buying the same posters over and over and over again, so I know there are more crazies out there. The difference is, they don't seem to care about price or condition. I do.
Lobby cards, that's a different story, because not everything I have is on my website, and I don't always have access to my spreadsheet, so I forget and re-buy. I have a lot of multiples there.
T