Damn, and I've always felt like I must have some kind of OCD whenever I'm getting a refresher on MVCC/MGA isolation levels and their guarantees and the associated auxiliary locking (say, select for update with lock in Firebird, for example) just to be sure I'm not writing something stupid. Simply not using transactions at all is something I can't even fathom. That's basically no better than blindly mutating shared in-memory data structures in a multi-threaded program. Who would write something like this?
Same thing here, our legacy codebase avoided using transactions, and to this day, after migrating to a new codebase, we still get reports from clients here and there about errors which stem from inconsistent data