That's one of Murphy's laws of electronics: "a three hundred dollar circuit board will fail to protect a twenty-two cent fuse..."
"After two days of troubleshooting, the most annoying person in the workplace will happen by, see the problems at a glance, and proceed to tell everyone in the office about it..."
"At least one wire in any made-to-length harness will be too short. An engineer will suggest cutting off more wire to fix it..."
"A dropped component will always fall into the place where it can do maximal damege..."
"Units of measure will always be given in the least useful possible units - i.e., a tape drive speed will be expressed in furlongs per fortnight..."
If I recall, there's three pages of 'em - I'll have to hunt and see if I can't OCR 'em...