The theory is what happens if you customize a toy in the toy story realm. I think that they become who you customize them to be, but they take time to get used to it. Evidence for the they become who you customize them to be part, is with Sid from the first movie where he sort of customizes toys? But not in the means I am talking about (what I mean by customizing is removing the factory paint and giving it your own complete makeover). For example we see toys with parts changed into other parts of other toys. It doesn't seem to affect them, but it could have affected them in a major way when it first happened. How would you react after waking up to see a drastic change in your appearance/body functions? Even WITH a slow process (That is how it is with toy customizing, slow process. (I know as I do toy customizing myself.)) I bet it would be scary at first, and then eventually you get used to it. Which is why I think that it would take some time getting used to.