The document discusses reasons why tongue twisters are difficult to say. It explains that tongue twisters contain conflicting syllable patterns, regular stress patterns across words, and similar sounding phonemes. This disrupts the rhythm and regularity of speech. Examples are provided to illustrate tongue twisters containing she sells sea shells, six thick thistle sticks, and rubber baby buggy bumpers and how their syllable patterns and stresses make them challenging to articulate smoothly.