Revealing the outcome in the prologue dilutes the story of any suspense. It is mandatory for any reader to read the prologue to know the basics of the story. And being told what is going to happen is like knowing that Darth Vader is Luke's father before you even watch the movies. I would prefer not to be told what happens in the story, because it gives the novel or section of writing the upper hand in obtaining and keeping the readers attention throughout the story.
Revealing the outcome of the plot in the prologue can be an effective technique for creating suspense, depending on the type of text we are reading. If the text is meant to conclude in a surprising or unexpected way, and the story is more about the outcome than about the journey, then revealing this conclusion could ruin the story. However, some stories reveal the ending at the very beginning, and this does not mean that the story stops being interesting. An example of this is the story "The Death of Ivan Ilyich."
