[kimi]

Apart from your unit tests, there is no such thing as "Messages do need to be strictly ordered and messages cannot be lost". You can WISH for messages to come in the right sequence, and even count on it in terms of optimization, but if an event tracks something that happened, and that event comes late - or after a week - your system cannot say "Too bad, I told you, only events in the right order here" (which, at this point, is invalid in itself, as you missed some).

[legulere]

If you want a reliable system it’s very important. Those concepts very much relate to Isolation and Consistency in ACID. Just take a look at different levels at https://jepsen.io/consistency

There are certainly fields with lower correctness requirements where inconsistent data is not such a big deal though.