One of the big masters of litterary criticism, Iser described the reading process as happening between two opposite trends: retention and protension. By protensions he meant the expectations any text creates in the reader´s mind. By retention, the somewhat frustrated experience of those expectations.
I think Iser´s protension refers to the evocative power of any text. The ability to bring ideas or images different than those in the written text. That happens because the product of any reading act is the conjuction of two souls, the one in the text and the one reading it.
What I want to tell with all this is that if you want your writing to be distinguished with beauty it has to be evocative. And being evocative means putting lots of protension in the act. And it means not trying to exhaust the topic you are writing about. Your writing should have loose ends. Let spaces for the reader.