Why do so many trials end up as tribulations?

I want to give Dave Kurlan of Objective Management Group the credit for stimulating this article. I’ve added a link to his original piece below.
Whilst trials have become an accepted and effective way of selling consumer or personal productivity software tools, many vendors suffer a far lower conversion rate in Enterprise environments.
Whether you think of them as trials, pilots or proofs of concept, these evaluations need to be managed far more carefully for complex software solutions if they are not end up as a frustrating and unsuccessful tyre kicking exercise.
As with so many other aspects of complex B2B sales, failing to prepare and plan typically means that you are effectively planning to fail…
One of the problems with evaluating a complex software solution is that there is almost inevitably “too much to see”, with the result that the prospective customer can end up confused, overwhelmed or underwhelmed