At the beginning of this century, Wigner put forward the theory of continental drift, which met with strong opposition because his theory was based on the assumption of unidentified forces sufficient to cause continental drift  We can now accept Wigner's theory
This is not because we have identified the power to cause the continent to drift, but because the new instruments eventually enable us to confirm the movement of the continent through observation
When an event assumed by a theory is confirmed, the theory can be accepted even if there is no explanation for the cause of the event.