Knowledge is a system of knowledge claims based on observation, tests, and proof. One can justify that one knows something when that can prove that the knowledge claim corresponds to an observable event, and one can cause that effect to occur; that is, one can predict the effect. The knowledge claim can then be said to be a concrete fact.
On the other hand, imagination denotes a mental image, a visual process similar to a movie.
In the context of knowing, we could call it a thought experiment: We visualize a scenario that mimics the process of performing an actual experiment, but simply imagining that experiment is not enough to make a knowledge claim.
Imagination is a creative process and is affected by many factors, for example, personal biases and beliefs. The product of that process results in a belief report rather than a knowledge claim. I may be splitting hair here, but the distinction between a belief report and a knowledge claim is critical to understand.
Belief reports are fictions until they are proven to be fact. In this sense, fictions can be thought of as if they are facts and function to fill the holes in theory, but they are not facts.
Sorry for the philosophical pontification. That’s the best I can do.