Single focus.
Since you’re aiming, then, at such great things, remember that you’ll have to exert no small effort to attain them, and that you’ll have to renounce some things altogether, while postponing others for the present. But if you want to have both these things and public office and riches too, you’ll quite possibly not even gain the latter because you’re aiming at the former too, and you’ll certainly fail to get the former, through which alone happiness and freedom can be secured.
Handbook 1.1(4).
Things within your control: that’s your only focus. The other stuff comes and goes with indifference, as a byproduct.