I knew I was a collector sometime between buying 
my first and my second cel.  My daughter is an 
anime enthusiast, and so after my first cel, I 
had a good opportunity to get her two inexpensive 
cels from CCS that would look good framed next to 
each other.  In time, I took them to a frame 
shop, where I and the owner tried out various 
colored background and frame mats to complement 
the colors in the cel.  

The first (of Kero-chan) was easy, since he's 
pretty much one color and simply drawn.  The 
second (of Sakura) was more complicated.  We 
tried combination after combination.  Then, after 
many tries, we hit on a light green background 
and a vivid red frame.  We put the cel into this 
combination and ...

... the expression on the cel visibly 
changed.

The frame store owner and I took the mats away 
and looked, and then we put them back behind and 
next to the cel ... and it happened again. 

"Well ... she's made her choice, hasn't she?" the 
frame store owner said, a little nervously.

So ironically, the cel that made the difference 
is no longer mine, but I knew after that 
experience that I was seriously a collector.

This is the cel (without the mats, alas).