Your biggest mistake as a collector?

[Nielsb90]

Let me explain the title with my own example:

I bought the Criterion release of The Third Man back when it was announced that it was OOP. Back then I didn't own a region A player and mainly bought it because people said it would be rare. When Lionsgate announced their release I sold my Criterion copy for around 35 dollars like an idiot! I didn't really realize what Criterion meant to people back then..

Anyway - have you waited too long to purchase a movie/release that is now very valuable? Have you traded in releases that you now can't get a hold of? Did you leave an amazing deal on the store shelf?