On the matter of confusing pain with evil (from Margaret R. Graver's Stoicism and Emotion):
This alternative (and philosophically preferable) explanation is expressed in the passage just quoted, in connection with the confusion between pain and the destruction of our nature. Pain, says Cicero, is thought to be an evil both because of its sharpness and because it is seen to accompany (videtur sequi) destructions of our nature; i.e., instances of harm to our natural constitution." Being injured is not at all the same thing as being in pain, yet because pain does regularly accompany injury, it is easy for the undeveloped mind to assume that it is the pain itself that is to be avoided. Hence the difficulty of persuading a child to accept some necessary but painful medical treatment. With greater experience of the world, the child may come to realize that there are two object types to be kept straight, those which cause pain and those which harm the body, and to regard these things in different ways. Until then, the frequency with which these co-occur will be misleading. Likewise pleasure comes to be understood as a distinct object type from that which promotes health, and good or bad reputation as distinct from reputable or disreputable conduct. Even life itself-that is, the mere continuance of one's existence as an animate organism-is to be distinguished from a proper object, the preservation of one's natural state or (as we might say it) of one's wholeness as a person. A mature person does not necessarily believe that death is to be avoided at all costs.
Margaret R. Graver. Stoicism and Emotion (pp. 160-161). Kindle Edition.