Here's why:
* Joking Tone: The phrase "yet at least tragedy was not without its value now one remembers to lock doors" is a sarcastic and humorous way of saying that a bad experience (presumably a burglary) has taught a valuable lesson, even if it was a negative one. This indicates a joking tone.
* Autumn: The statement doesn't directly mention autumn, so there's no way to determine if the word "autumn" would be appropriate.
To clarify, let's consider a potential scenario:
Imagine someone had their house broken into. They might later say something like, "Well, at least I learned to lock my doors now!" This is similar in tone and meaning to the statement in your question. It's a way of finding humor in a negative situation.