That's a fun challenge. It was hard to try to summarize the motivation behind the idea of antifragility in such a restricted vocabulary. Here is my attempt:
Things sometimes break. This happens when outside forces cause bad changes to it and to the world it acts in. Things that this can happen to are not things you can put much trust in. It would be a lot better to have something that does not change because of things happening to it, or even better, one that gets better the more those bad things happen to it. It is a good idea to make the things you have be of this sort, but that can not be done all of the time. To find things that match this idea is not easy, but it is true that there are some situations in the real world where this does happen.
I think you want to separate out "bad" from change.Things sometimes break, this happens when outside forces cause changes to it and the world it acts in. We call a thing fragile when most changes are bad from the perspective of the thing. EG ice is fragile because changes in temperature, motion, etc. will cause it to break. Anti-fragility is when the thing is designed such that the biggest possible changes do not break it.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.