The Stoics thought that knowledge depends on a special kind of appearances which they called ‘apprehensive’, which are by definition true. Interestingly, Sextus Empiricus reports in M 7.247 that they held that there are appearances that are true but that are not apprehensive because they are true merely by chance and thus cannot constitute knowledge. I believe that this suggests that the Stoics were aware of what is in modern literature known as the problem of epistemic luck. Unfortunately, Sextus’ report (...) leaves out a lot of important details, which makes it difficult to understand exactly which appearances the Stoics thought are true by chance, and why. I argue that the true non-apprehensive appearances in question here are imaginations, representational states which are not immediately caused by external objects through perception, but produced solely by the mind. I propose an explanation why the Stoics, who defined chance in terms of hidden causes, would have thought that imaginations can only be true by chance. The explanation stems from their view that the essential characteristic of imagination is that it leaves the actual cause of its representational content hidden from the subject. (shrink)