Here is a quote from Elisabeth Elliot on Psalm 16:5:
"I know of no greater simplifier for all of life. Whatever happens is assigned. Does the intellect balk at that? Can we say that there are things that happen to us that do not belong to our lovingly assigned "portion." ("This belongs to it, that does not")? Are some things, then, out of the control of the Almighty? Every assignment is measured and controlled for my eternal good. As I accept the given portion other options are canceled. Decisions become much easier, directions clearer, and hence my heart becomes inexpressibly quieter. A quiet heart is content with what God gives."
I highly recommend this book for anyone who struggles with discontentment, anxiety, or worry. It has really given me a lot to think about and has challenged me in many ways.