Some people become overwhelmed when they feel they have too many things to do and they don't have enough time to do them. This overwhelmed feeling causes them to move more slowly than they usually do. Their minds becomes unclear. It's hard for them to focus and concentrate. Instead of becoming more efficient at what they have to do, they act way below their standard competency level.
What is the solution? Serene zrizus!
What does it mean to have serene zrizus? It means that you take action, and you do so with full speed ahead while remaining calm and tranquil inside. You move as fast as is appropriate for the specific situation and circumstance. But you have peace of mind.
You might not have previously associated zrizus with serenity, but now you can. Your mindset acknowledges that you will do everything that you have to do and that you will have an inner calm. Although you might move quickly, inwardly you are at ease.
A key benefit of having serene zrizus is that you think clearly. You think about what you need to do, and you remain calm as you take action.
([From Rabbi Zelig Pliskin's book: "Taking Action" - pages 55-6] (Artscroll.com)