In this book, Jeffers presents a lifestyle where you learn how to reject worrying over uncertainty while learning to embrace the adventure on not knowing what is to come while importantly realizing that so many of life's circumstances are beyond our control, no matter how much worry we invest in them. There are forces far greater than us in life, she calls it the Grand Design, others of us simply call it God. Whatever semantics you use, it is all the same. We believe we are in control of every aspect of our life. We do control much, but also not so much. This is where the book delves into, learning to control what we can control and focusing on that while giving up the reins and becoming a neutral observer to those circumstances we cannot control.
We cannot control other people, the economy, the prospect of death, politicians, the weather, but these are all examples of things people stress and worry about. If it starts to rain, let it.
Do not attach to predetermined expectations. So much of regret comes from that. The expectations were formed before knowing all the various circumstances that you had to deal with.
The trick is, control what you can. Go about your day with your best effort. Work hard, do good by others. Those things are generally in your control. The rest, you should care about however recognize you do not control them so stop the worrying. Let life in that respect come to you. With that, there will be more peace.