"Can you have complex characters and situations in a short story?"(Catriona)
A short story does not have to be simple, or about a single incident. If the fiction works then the reader attends to the imagined world not the form. And an imagined world does need characters that you can see and believe in. For me, a good short story is as memorable and imaginatively real as a good novel. The imaginative energy that goes to make it is much the same.