the preface of《A Brief History Of Time》：
We go about our daily lives understanding almost nothing of the world.
We give little thought of the machinery that generates the sunlight and makes life possible.
To the gravity that glues us to the earth that would otherwise send us spinning off into space.
Or to the atoms that which we are made.. and on who’s stability we fundamentally depend.
Few of us spend much time wondering why nature is the way it is.
Where the cosmos came from.
Whether it was always there.
If time will one day flow backward.
Or whether there are ultimate limits to what humans can know.
What is the smallest piece of matter.
Why we remember the past and not the future.
And why there is a universe.