Now.

Now is no time
to think of what you do not have.
Think of what you can do
with that there is.
- Ernest Hemingway

There is nothing else than now. There is neither yesterday, certainly, nor is there any tomorrow. How old must you be before you know that? There is only now, and if now is only two days, then two days is your life and everything in it will be in proportion. This is how you live a life in two days. And if you stop complaining and asking for what you never will get, you will have a good life.
- Ernest Hemingway, For Whom The Bell Tolls