Can query fail in production?

Oren Eini has commented Davy Brion’s post "There Is No Excuse For Failing Queries In Production", and I found his comment quite important. On contrary, you must remember any query may fail in production.

Imagine: even Davy, who wrote an excellent sequence of posts describing how to implement your own DAL, can forget about this. So the topic is definitely important enough to be re-posted here ;)