Dave Kellog:

In the end, there are two types of things that CEOs can potentially stress about:

• Things they can control. They shouldn’t stress over these because they should do something about them, instead.
• Things they can’t control. They shouldn’t stress over these because doing so will not change the outcome. Worse yet, it may well change the outcome — for the worse — over the things they can control.

Ergo, CEOs should never stress about things. QED.