At some point, you just have to let go of what you thought should happen and live in what is happening. - Anonymous
I love this, because you can live fully in what is happening and still work to change what you can, where you can. In Buddhist terms, it is called being fully present - not wallowing in the past and not obsessing about the future. One can be aware of both past and future, and use that awareness to guide the present, but, in the end, now is all that is real and true for each individual.
I love the concepts I learned in my youth that all is present unto God and that time is measured only unto mankind. A huge part of my peace has come through allowing myself to live in what is happening, not in the future or the past.