If X exists, then Y must also exist. Likewise, you can infer that certain other things must follow from the very existence of the premise. Essentially, you're being Sherlock Holmes with your own creation. This fact infers that fact which in turn infers other facts. If this event takes place, then other events must follow from it.
Every act has implications and repercussions.
Explore it not only in the physical sense but in the psychological and moral aspects as well. They have to be able to believe your story at least while you're telling it. The reader must be made to ask, 'Yes. . .yes. . They must be able to tell a story using a sequential series of panels and one panel must lead to another and it must seem effortless. Storytelling starts with the writer, with the same process I described above.