There is a famous example, thought up by the contemporary American philosopher Robert Nozick, which helps to show this. He imagines that a machine has been invented, which by affecting your brain, can give you any kind of experience you like. The only snag is, you have to plug in for a lifetime or not at all. Do you plug in or not?

I think sensible people are at least going to think very carefully before they plug in. Sensible people are not going to choose, or program for themselves, lives merely of pleasant physical experience, the constant experience of being massaged on a beach, drinking daiquiris, leaving out the experience of getting sand inside your swimming costume. That would obviously be a waste of the marvellous machine, and might easily get boring. No, you'd program it to allow you to experience things that are really worth while, even if they involve difficulties: the satisfaction of struggling to do a good and worthwhile job, raise a family, achieve something, contribute something. You could have the experience of many years of effort to produce the world's finest symphony, for example, and eventually conducting it in person at the Carnegie Hall – and only then retiring to the beach for a time.

But once you start thinking in this more sensible way about what experiences are better – the experience of struggle and achievement, for example, above the experience of the beach and the daiquiris – you realise that experiences are not what you want. You don't want to feel as if you've written the world's greatest symphony, if your ambitions and talents lie that way – you want to write it. And if you're sensible you'll realise that the chance of really doing it, however small, here in real life, is infinitely better or more important than experiencing an illusion of doing it on the experience machine. Life on the experience machine is no life at all, because it stops you from being able to do anything.

I'm not saying that if the experience machine became available no one would use it. Some people would — just as even today we see drug addicts, people chasing the dragon, chasing experiences, people who can't face up to reality and to struggling to get real things done. But we feel sorry for them — and I think we would, and should, feel sorry for anyone who linked up to the experience machine.

As we said the other day, quoting the very ancient Greek philosopher Heraclitus: It is not good to think or act like men asleep, for the waking have one common world, while dreamers go off, each to his own. The "world" of the dreamer is no world: the actions of the dreamer are no actions: the achievements of someone on the experience machine are no achievements at all. A life of merely "having a good time" is not really a life, so having a good time can't be the point of life.

Christopher Martin teaches philosophy at the University of St Thomas in Houston, Texas. Email: martincf(at)stthom.edu