Prefixes are additions to root words that change the meaning of the word. In English these prefixes are not uniform in their alteration of meaning. For example take the prefix “in-.” In- can have both positive and negative connotations. Add in- to the word “credible” and you have incredible, which carries a positive connotation. Add in- to the word “competent” and you have incompetent, which carries a negative connotation.
This is what I think of when I am bored.