The Stoics, such as Marcus Aurelius in his Meditations, point out that there are things we can change and things we cannot, things we can control and things we cannot.
What we can change and control, we can act upon, to the best of our ability and in accordance with our highest values, ethical principles, and the best of our knowledge.
What we cannot change or control, we can only accept.
Not to accept what we cannot change or control is to suffer since to mistake what we cannot control for what we can control is delusion. Trying to make delusions fit reality is like trying to fit a circle into a triangular hole. No amount of effort will make it fit; the only fruit of our efforts to try will be exhaustion from our profitless exertion.