In the original oz books, the heart and brains given to the tin woodman and the scarecrow are placebos given to them to make them feel better, as they already had the qualities they were looking for from receiving those.

But throughout the series we meet many more crafted people (not sure what exactly the fandom term is), whose brains and hearts appear to do something. The seeds in each of Jack Pumpkinhead's heads consist of his brains and he says he knows he needs a new head when he feels them shift as the inside rots. Tik-Tok's metal brains require to be wound frequently in order for him to function. the glass cat's narcissism is blamed on having a brain too fancy and a heart made of ruby. the patchwork girl's erratic behavior and lack of social filter is blamed on her brains being unbalanced due to Ojo just dumping a bunch of brain material in it, and her apparent lack of empathy (which isn't entirely true) is blamed on her lack of a heart.

Is it all just confirmation bias/a placebo?

What do you think?