Using an unsigned variable in a computer program can lead to unexpected errors which we call overflow errors.
This where if we subtract one from the variable when it is 0 it becomes an unexpectedly large number like 4294967295.
This is a /wiki/spaces/IX/pages/2053242952which is relatively harmless although alarming looking.
But it’s also the same problem that caused the French Ariane rocket to explode (a $500 million dollar disaster - see https://www.bbc.com/future/article/20150505-the-numbers-that-lead-to-disaster).
It’s also mostly likely the true reason behind the 1.2 billion dollar lawsuit that Toyota settled with respect to the so called pedal accelerator problem. Software was the much more likely culprit rather than the type of plastic they used.
Google around and you’ll find all sorts of expensive problems that arise from this issue.
How does it happen? Read about how computers handle subtraction.