The Stoic dictum that we should concern ourselves with things in our control, and not with those outside of our control is wise, but demanding. Perhaps too demanding. Initially, it seems, all that is beyond our control was to be considered indifferent. Wisely as well, I think, the absolute nature of this directive was qualified. Certain of the Stoics began to note distinctions in the vast multitude of things seemingly beyond our control. Some of them therefore came to be considered worthy subjects of concern, or at least of more concern than others.
These included matters related to health of the body, for example. The tendency of ancient philosophers (and some not so ancient, unfortunately) to distinguish between mind and body, which was carried over into Christianity and beyond, made concern with the body seem unimportant. However, the rather intimate relation between what was considered mind and what was considered body eventually compelled Stoics and others to recognize that problems with the one could result in problems with the other, and so a concern with health became, however grudgingly, considered as more than a matter of complete indifference.
Human nature has always presented problems for systems of thought which seek to establish finality, certainty, single causes, single goals, single truths. The same may be said of all of nature. This is because we humans, and the rest of the universe we inhabit, are far more complex than we like to think. It's odd that the "quest for certainty" is often associated with religions or the religious. One would think that the belief in a great, all-powerful and all-knowing creator would instill in us a recognition of our own limitations, including limits on our knowledge and ability to know. In certain instances it does, but those instances seem to involve only the recognition by some of us of the glaring limitations of others. Such is the extent of our self-conceit that we assume God has created the universe and formulated a purpose for it and us obvious enough for us to discern, and indeed made it in such a fashion peculiar enough that we humans are destined to rule over it.
This view can make even the supposedly humble seem breathtakingly arrogant. Someone decided to make audio books of some of Chesterton's Father Brown stories, and I've heard them now and then through the good offices of satellite radio as I drive about. It may be that it is the manner of the actor portraying the good priest, but I'm struck by the smugness of the character far more than I was when I read the stories. Chesterton himself shared this smugness, of course. Smugness is not a characteristic of the humble or of those who acknowledge their own limitations.
Which brings us back to things in our control, and things out of our control. Even when qualified, this is a consideration which requires a recognition of our limitations; of what we can and cannot do, and the futility and indeed destructive nature of an excessive concern with people and things which we can't shape to our desires. It may be said to be the first step towards practical wisdom. Stoicism is in many senses a therapeutic philosophy, as it seems has become known to psychologists who have noted similarities between it and cognitive behavioral therapy. Ultimately, to the extent we can control things that control is limited. But this control implies responsibility as well as the acknowledgement of our limits. Because we can control ourselves we are responsible for ourselves and our conduct; we should not blame our conduct on what we cannot control just as we should not base our conduct on what we cannot control.