I'm not sure that follows just from adding your own ancedata ;). I've made my share of mistakes at every job, and haven't gotten managed out. What will get you fired is consistently under-performing, persistent personality conflicts, or repeated negligence without visible improvement.
Your company might be too lazy to have any sort of formal training program, but that cuts both ways - they'll be too lazy to hire a replacement if you're showing signs of improving, too. Your manager probably has too much on their plate to train/mentor you themselves, but I work places where coworkers like talking shop, and will generally be happy to share advice, techniques, thought processes, etc. - especially if it means they're enabling you to take things off of their plates to get more stuff done.
Now, granted, this isn't everywhere, but it's far from being OC's "unrealistic" either.
Aye and thanks for the contribution to that effect/effort.
Maybe one day we'll get to a point where this is normative in the industry (and it's my earnest, strident hope that we do).
As far as could tell, they weren't saying it didn't happen to you but to infer that's (generally) not how things work elsewhere. For example, if you've never heard of the phrase "being managed out"[0,1,2], you're lucky, but others haven't been and will continue to not be for some time.
You're preaching to the choir, essentially. :)
[0] - https://www.linkedin.com/pulse/getting-managed-out-fired-wel...
[1] - https://www.mattgingell.com/managed-out-at-work-a-guide-for-...
[2] - https://www.ronankennedy.ie/blog/2017/1/16/am-i-being-manage...