Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That's relativity.

Speak only if it improves upon the silence.

Live as if you were to die tomorrow. Learn as if you were to live forever.

Life is like riding a bicycle. To keep your balance you must keep moving.

The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it.

The secret to creativity is knowing how to hide your sources.

There are many causes I would die for. There is not a single cause I would kill for.

Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution.

You should be the change that you want to see in the world.

Science without religion is lame, religion without science is blind.

The United States invariably does the right thing, after having exhausted every other alternative.

Seven social sins: politics without principles, wealth without work, pleasure without conscience, knowledge without character, commerce without morality, science without humanity, and worship without sacrifice.

It takes 20 years to build a reputation and five minutes to ruin it. If you think about that, you'll do things differently.

It has become appallingly obvious that our technology has exceeded our humanity.

If you think a thing is impossible, you'll make it impossible.

I love deadlines. I like the whooshing sound they make as they go by.

It does not matter how slowly you go so long as you do not stop.

All warfare is based on deception.

If we knew what we were doing, it wouldn't be called research, would it?

The Rich must live more simply so that the Poor may simply live.