This has happened to me several times, albeit at a much smaller scale. I fire up a few GPU instances for training neural networks and when I got to shut the instances down I forget that you always need to refresh the instance page before telling AWS to stop my instances. I still go through all the confirmations saying I do, indeed, want to stop all instances. However, these few times I forgot to refresh to make sure they actually were shutting down and simply went to bed. Not an $80k mistake, but certainly a couple hundred dollars, which hurts as a grad student.

Now I have learned, _always_ refresh the page and instance list prior to shutting anything down and _always_ confirm the shutdown was successful.