One way that Spinoza seems to be clearly drawing on the Stoics is in terms of recognizing that we are sorrowful about events because we suppose that we have some power to make them otherwise when we do not. The Stoics counsel us to seek to understand causes so that we might understand what outcomes we can affect and which we cannot, what aspects of the world we can control and which we cannot, to focus on those that we can and to recognize that those we cannot are just part of the order of things and to accept them accordingly.
The problem I was realizing as I was getting myself organized for the new semester and setting myself some intentions for the semester–thinking about how not to worry about things that are out of my control and to only work on those that were within my control–is that anxiety comes from not being able to know which is which. I can understand why the Serenity Prayer ends with a request for wisdom to know the difference between the things that we can change and the things that we cannot. My entire anxious life is rooted in wondering if I did something that adversely affected some situation that I might otherwise have thought I had no control over or whether I should have done something in order to bring about some desired goal that I might have thought was not in my control.
Seneca writes that nothing happens to the wise man contrary to his expectations because he recognizes when his efforts can be thwarted. But that would really seem to be all the time, which is to suggest that one’s plans may be in her control but the success of them always depends on the order of the nature and fate. For the Stoics, the actions that we control are themselves part of a larger order of nature. So our control is even then in affirming them as part of that order. The good Stoic then tries to fit into that order of what will be. Here it seems that the Stoic understanding of our action involves a sense of time that sees the action we contemplate as something that already fits within the order of the universe. The wise man acts in a way that knowing the causes of the universe can conform to its order. Such a way of acting seems to involve that we already know how our action fit into the universe. Our problem is that we cannot yet understand the causes of what has not yet happened. I think this is what Arendt means by the newness of action, and why Kant makes the responsibility to the duty and not the outcome, and yet it is the outcome that we want to achieve. This is why we can never fully understand the causes and as a consequence can never fully know what is in our control and what is not in our control. What is not in our power it would seem is the wisdom to tell the difference.