Suspense is what makes the reader want to know what's coming next. Coincidence and chance play a part in suspense and plot. Plot is the simplest element of fiction. Character is, perhaps, the second. It's a toss-up whether symbol or theme is third.
Symbols are figures of speech which have a value in themselves, but also an additional meaning.
A flag is a nice piece of patterned cloth which can decorate a wall or hang on a pole outside somewhere. It also can be symbolic of patriotism. An escape story supplies a surprise ending more often than interpretive stories do. Happy endings are nice, but indeterminate endings are more like real life. Happy endings may be satisfying, but they do not make readers think.