Most people who use family tree software have fairly regular families. Mother, father, brothers, sisters etc. Occasionally there might be a hiccup when there are in-laws and step-relations, but generally the software is sufficiently flexible to take these into account.
Then there’s incest. Here’s the tale of a software developer who apparently received a complaint from a customer who found that the program wouldn’t let him enter the details of the two children he had with his own daughter.
The discussion that follows the initial problem is priceless. Some people gamely attempt to focus on the programming problem, while others let rip about the whole icky incest thing. Someone points out, rather usefully, that incest is more common than many people realise, and was especially so back in the 17th and 18th centuries.
Anyway, the problem eventually got solved, thankfully. I guess that’s one less worry for Philip Garrido when he eventually gets his hands on some of this software.