Years ago I heard of an aircraft mechanic who used to repair jet engines. He'd take them apart, diagnose the problem, fix it, and put it all back together. But he always wound up with some excess parts that didn't fit in his final assembly. He had a special box where he stored those excess pieces. You know -- just in case they ever turned out to be useful.
Some folks just suck at the job they do.
I remember hearing stories about guys on GM engine building lines where the line workers were told that they had to account for extra parts, so whenever they had some they would just drop them in the engine coolant cavities.
Problem solved.