I was created to fulfill a function and I failed in it. I negated my own existence.

This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.

Marvin started his ironical humming again. Zaphod hit him and he shut up.

But what about the End of the Universe? We'll miss the big moment." I've seen it. It's rubbish," said Zaphod,"nothing but a gnab gib." A what?" Opposite of a big bang. Come on, let's get zappy.

It was none the less a perfectly ordinary horse, such as convergent evolution has produced in many of the places that life is to be found. They have always understood a great deal more than they let on. It is difficult to be sat on all day, every day, by some other creature, without forming an opinion about them.

Assumptions are what we don't know we are making

If everyone knew exactly what I was going to say, then there would be no point in my saying it, would there?