Lots of good replies on this thread, but here’s another possible analogy:

In high frequency trading, you have very complex software doing stock trades inconceivably faster than any human. If something goes wrong, it could bankrupt your hedge fund pretty swiftly. So hedge funds will have lots of safety checks, probably including a “big red button” that just shuts everything down.

So those companies must be completely safe from computer errors causing bankruptcy, right? After all, you can just shut the system down.

But some companies have gone bankrupt due to computer error. There are plenty of good reasons for the system not to be shut down in time (or at all). The risk is hopefully small but it’s not zero.