Susan hates when the underwire in her brassiere breaks free from the confines of its fabric prison and pokes her in the armpit. She enacts the flawed plan of pushing it back in place until she eventually pulls it out completely. Once gone she wonders why the underwire was even necessary. She doesn't have a Rosalind Russell physique, just little B-cups and they certainly don't require much to hold them in place.
Susan managed quite happily for a week or so without the underwire in her left cup until she got poked by the right cup. Based on her previous success she pulled out the remaining underwire and immediately figured out why it was necessary.
Without the structure underwire provides, Susan's brassiere is like a flaccid sack into which she throws two oranges.