From Dirk Gently's holistic detective agency :

‘We’d had it thought out for us. We had with us some very specialised devices for helping us to continue to believe in the purpose of the trip even when things got difficult. They generally worked very well, but I think we probably came to rely on them too much.’ ‘What on earth were they?’ said Dirk. ‘It’s probably hard for you to understand how reassuring they were. And that was why I made my fatal mistake. When I wanted to know whether or not it was safe to take off, I didn’t want to know that it might not be safe. I just wanted to be reassured that it was. So instead of checking it myself, you see, I sent out one of the Electric Monks.’