"wrong assumptions, no market for the product, etc"
Been there, done that!
However, to stick to the subject of databases - I found later in my career that the really alarming events are more to do with having data you shouldn't have rather than not having data you should.
NB The only one of these that I'm going to admit to involved a demo application being sent out on CDs to hundreds of thousands of end-users by IBM and sample data sourced from a particularly unpleasant alt.* newsgroup - I was CTO and when an engineer approached me and rather sheepishly told me that some of the same data had gone to IBM I had a very bad moment indeed.
However, on investigation it turned out the only thing that did go out on the CD was the single word "sheep".
At a startup earlier in my career, we generated an email address for every customer which they could use to interact with our system. The CEO wrote a script to pick words at random from the Princeton Wordnet database.
One afternoon I thought, wait a minute, what's actually in Wordnet?
Needless to say, many apology emails were sent later that day.
In recent years, I created a homework assignment for a security class where the student's job is to crack a set of password files. First easy, un-salted hashes, then salted hashes, ... etc.
To illustrate the badness of using dictionary words as a password, I randomly generated a unique password file for each user by sampling from /usr/share/dict/words.
> One afternoon I thought, wait a minute, what's actually in Wordnet?
I know exactly how you feel. It took me about 5 minutes to find Shutterstock's list of dirty, naughty, obscene, and otherwise bad words [1], and about 20 more minutes to add a blacklist check to my script.
Fortunately none of the students had actually been given a bad word. Whew!
Been there, done that!
However, to stick to the subject of databases - I found later in my career that the really alarming events are more to do with having data you shouldn't have rather than not having data you should.
NB The only one of these that I'm going to admit to involved a demo application being sent out on CDs to hundreds of thousands of end-users by IBM and sample data sourced from a particularly unpleasant alt.* newsgroup - I was CTO and when an engineer approached me and rather sheepishly told me that some of the same data had gone to IBM I had a very bad moment indeed.
However, on investigation it turned out the only thing that did go out on the CD was the single word "sheep".