This is a sentence fragment. A full completed sentence with this wording would be "If your parents think today's fashions are weird they should see the clothes people wore in the middle ages."
This is not a complete sentence, when a sentence is fragmented it has disconnected from the main clause. The best way to fix a fragment is to remove the period from the two sentences if they are together.
Other types of punctuation are allowed for sentence fragments such as commas.
Behavior can cause a lack of self-confidence by making people avoid situations where they would gain important knowledge or experience that often help confidence grow.
The title of the story includes the word fall which foreshadows the ending of the Usher family line. The decreped state of the house described in the begining foreshadows the dissolution of the Usher family.
