I feel like many people downplay how important this is. I've wasted way too much time because of this. Doing code archeology to understand why data persisted to database many years ago breaks some seemingly unrelated feature for a customer is definitely not my favourite part of the job. Working on a validator that someone was "too busy to add" in the first place is also not fun (and a waste of time - because original author could probably do this in matter of minutes; whereas someone fixing things post-factum need to reverse engineer what is going on; check whether some funny data wasn't persisted already and potentially handle it).

To phrase my frustration in more constructive way: it's always a good idea to put explicit constraints on what you accept (What characters are allowed in text-like id - only alphanum? Only ASCII? What happens with whitespace? How long can it be?). Otherwise it's likely you will find some "implicit" constraint down the road; ie. other piece of code breaking down.