The metaphorical “what if we killed Hitler before he became Hitler”
In studying history, we are restricted by practicality to study only such things that concretely happened. Surely this leads to something like survivorship bias, so we could be placing undue scientific emphasis on things which were unlikely given material conditions, yet occurred nonetheless.
Therefore some level of speculation is necessary I think, in order to learn from the things which went right due to the non-occurrence of events. Like the eternal dilemma of system admins, the proof of their usefulness is nothing happening, things not breaking, which in turn appears as proof that they were unnecessary in the first place.
Best I can come up with is the handful of averted nuclear deployments during the Cold War, but those are fairly well known.
The Carrington Event occurred before usage of electricity was so ubiquitous. If a coronal mass ejection of that size or larger were to happen now, large sections of the planet could be without power for weeks. Given how dependent we are on electricity, that could lead to a societal collapse.
Ooh the wiki page also mentions a July 2012 solar storm that was Carrington level but just missed hitting the Earth in orbit. Another good contender for this thread.