Why is it called "fun size"?

I'm a big fan of imposed portion control. I obviously don't have the will power to stop eating so I like when things come in nice little single serve amounts. I LOVE 100 calorie packs. Look in my cabinet today and you will probably find at least 7 different items packaged in perfect 100 calorie portions. If I sit down with a bag of chips, I usually eat the whole (or at least half) of the bag. So it works for me to have these snacks so easy to grab and I know that I won't binge.
I tried to apply that logic to all foods thinking that "Fun Size" candy bars are sort of the equivalent of the 100 calorie snack pack, but I learned yesterday that the same principle does not translate to candy! I love chocolate and especially candy bars. Occasionally I will succumb to the display at the checkout line and buy one on my way out of the grocery store. I eat my 1 candy bar, it is good, I enjoy it, it is done. I never buy 3-4 candy bars and binge on them, just 1 and I am satiated with that. So why is it that yesterday I found myself eating 1 after another "fun size" kit-kat bar out of my daughters Halloween candy bucket? I stopped after I consumed 6 minis bars and realized I had just eating 3 full size candy bars! Wow, I'm just glad I stopped when I did.