It's true that, once you make a specific choice, other choices that you could have made in its place are gone. Once one possibility becomes actual, the other possibilities that could have taken its place are gone.

But some possibility has to become actual at some point. Otherwise you aren't living at all. Life is making choices and living with the consequences. Dreaming is nice, but it's not the same as living. And if you spend all of your present imagining possible futures, you never have an actual life.

In other words, what fills the void where possibility once lived is actual living.