You know serendipity can be a subtle but major influence on how people find things in libraries? Here's a situation where serendipity backfired.
A patron came up to the desk and asked if we had any books on how family members can cope with someone who has a drug and alcohol addiction. I brought her to a catalog workstation and did a simple book search for "alcohol addiction" - the second result was:
The patron didn't comment on it, and I quickly pressed on to find useful resources for her. I have no idea what her situation was, but still, I felt like an ass. Oh well.