What would have been the fate of sages if there were no fools?

Happy is the soul that has a friend. Happier is the soul that trusts in the truth of the heart of a friend. Happiest is the soul that knows the solemnity of friendship and honours its laws.

To be happy, you have to risk being unhappy.

Like love, like talent, like any other virtue, like anything else in this life, happiness needs to be nurtured - this is the truth of the whole matter.

The face of a truly happy man seldom lacks smiles.

Always be happy, you never know how happy you can make another by just being happy.

Happiness springs up from within. Do not seek it without.

It is better to hope less than to be hopeless.

Where would we have been without the discoveries of our predecessors, and where are we going without your discoveries?

Knowing trees, I came to realize, understand and appreciate the act of patience.

If your failure is not a lesson, it's indeed a failure.

Your time keeps flying away into vanity while you dine with your distractions. Your life keeps diminishing while you waste your time feeding your distractions.

Public sentiment is everything, said Lincoln. With public sentiment, nothing can fail. Without it, nothing can succeed.

Peter Ustinov was the first really positive influence in my career. He was real and he bore witness to it. The things he said to you, he lived them.

Maybe being powerful means to be fragile.

Philosophy is the love of wisdom: Christianity is the wisdom of love.

Nothing makes me roll my eyes faster than a "Coexist" bumper sticker.

War is nothing but organized murder.

I left the government because I saw the only way to get family planning moving, was to do it outside the government. I was never disillusioned with government.

It's such a deliberate thing to sit down and write a tweet. You're putting yourself out there in a very deliberate way, and over however many tweets, you start to create a character for yourself.

In recent years, more and more of my time has become absorbed by administrative work for the research council of ETH-Z of which I am presently the president.