“Be a sadist. No matter how sweet and innocent your leading characters, make awful things happen to them—in order that the reader may see what they are made of.”
One thing I like about this quote is how it challenges both the character and the reader to discover “what they are made of.” That “they” can work on multiple levels—making this quote both straightforward and yet layered.
Interestingly enough, this is just one of Vonnegut’s eight tips for writing (number six, specifically.) He’s not the only writer to dish out eight tips—seems like a comfortable number for a lot of us. You can read all of Vonnegut’s eight and the eight tips from other great authors over at this post.