This is from Joel on Software and yes, I had to laugh

“Custom development is that murky world where a customer tells you what to build, and you say, ‘are you sure?’ and they say yes, and you make an absolutely beautiful spec, and say, ‘is this what you want?’ and they say yes, and you make them sign the spec in indelible ink, nay, blood, and they do, and then you build that thing they signed off on, promptly, precisely and exactly, and they see it and they are horrified and shocked, and you spend the rest of the week reading up on whether your E&O insurance is going to cover the legal fees for the lawsuit you've gotten yourself into or merely the settlement cost. Or, if you're really lucky, the customer will smile wanly and put your code in a drawer and never use it again and never call you back.”

Check link here

It had happened to me, hrm, lemme think, probably more than three times. One of the projects was a really expensive one and right after the very few deployments it was never used again. For me that was deeply saddening as we had invested so many hours of work in it, the customer did pay, but sometimes you prefer seeing your software being used, even abused, rather than gone to the oblivion.