„And remember, my sentimental friend, that a heart is not judged by how much you love, but by how much you are loved by others.“
this is a line spoken by Frank Morgan's depiction of the Wizard of Oz in the 1939 film, which debuted 20 years after Baum's death. It did not actually appear in the "Wonderful Wizard of Oz". The ending of "Steam Engines of Oz" wrongly attributes this phrase to Baum when it would've originated from the 1939 adaptation script writers Langley/Ryerson/Woolf.
Variant: A heart is not judged by how much you love; but by how much you are loved by others
Source: The Wonderful Wizard of Oz